Add documentation and update README

Playgrounds/NetworkImage.playground/Pages/Creating_custom_network_image_styles.xcplaygroundpage/Contents.swift

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+//: [Previous](@previous)
+
+import PlaygroundSupport
+import SwiftUI
+
+import NetworkImage
+
+/*:
+ To add a custom appearance, create a type that conforms to the `NetworkImageStyle` protocol. You can customize a network image's appearance in all of its different states: loading, displaying an image or failed.
+ */
+
+struct RoundedImageStyle: NetworkImageStyle {
+    var width: CGFloat?
+    var height: CGFloat?
+
+    func makeBody(state: NetworkImageState) -> some View {
+        ZStack {
+            Color(.secondarySystemBackground)
+
+            switch state {
+            case .loading:
+                EmptyView()
+            case let .image(image, _):
+                image
+                    .resizable()
+                    .aspectRatio(contentMode: .fill)
+            case .failed:
+                Image(systemName: "photo")
+                    .foregroundColor(Color(.systemFill))
+            }
+        }
+        .frame(width: width, height: height)
+        .clipShape(RoundedRectangle(cornerRadius: 5))
+    }
+}
+
+/*:
+ Then set the custom style for all network images within a view, using the `networkImageStyle(_:)` modifier:
+ */
+
+struct ContentView: View {
+    var body: some View {
+        HStack {
+            NetworkImage(url: URL(string: "https://picsum.photos/id/1025/300/200"))
+            NetworkImage(url: URL(string: "https://picsum.photos/id/237/300/200"))
+        }
+        .networkImageStyle(
+            RoundedImageStyle(width: 200, height: 200)
+        )
+    }
+}
+
+//: [Next](@next)
+
+PlaygroundPage.current.setLiveView(
+    ContentView().frame(width: 500, height: 500)
+)

Playgrounds/NetworkImage.playground/Pages/Customizing_network_images.xcplaygroundpage/Contents.swift

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+//: [Previous](@previous)
+
+import PlaygroundSupport
+import SwiftUI
+
+import NetworkImage
+
+/*:
+ You can customize a network image's appearance by using a network image style. The default image style is an instance of `ResizableNetworkImageStyle` configured to `fill` the available space. To set a specific style for all network images within a view, you can use the `networkImageStyle(_:)` modifier.
+ */
+
+struct ContentView: View {
+    var body: some View {
+        HStack {
+            NetworkImage(url: URL(string: "https://picsum.photos/id/1025/300/200"))
+                .frame(width: 200, height: 200)
+            NetworkImage(url: URL(string: "https://picsum.photos/id/237/300/200"))
+                .frame(width: 200, height: 200)
+        }
+        .networkImageStyle(
+            ResizableNetworkImageStyle(
+                backgroundColor: .yellow,
+                contentMode: .fit
+            )
+        )
+    }
+}
+
+//: [Next](@next)
+
+PlaygroundPage.current.setLiveView(
+    ContentView().frame(width: 500, height: 500)
+)

Playgrounds/NetworkImage.playground/Pages/Displaying_network_images.xcplaygroundpage/Contents.swift

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+//: [Previous](@previous)
+
+import PlaygroundSupport
+import SwiftUI
+
+import NetworkImage
+
+/*:
+ You can use a `NetworkImage` view to display an image from a given URL. The download happens asynchronously, and the resulting image is cached both in disk and memory.
+ */
+
+struct ContentView: View {
+    var body: some View {
+        NetworkImage(url: URL(string: "https://picsum.photos/id/237/300/200"))
+            .frame(width: 300, height: 200)
+    }
+}
+
+/*:
+ By default, remote images are resizable and fill the available space while maintaining the aspect ratio.
+ */
+//: [Next](@next)
+
+PlaygroundPage.current.setLiveView(
+    ContentView().frame(width: 500, height: 500)
+)

Playgrounds/NetworkImage.playground/Pages/Displaying_network_images_UIKit.xcplaygroundpage/Contents.swift

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+//: [Previous](@previous)
+
+import PlaygroundSupport
+import UIKit
+
+import NetworkImage
+
+/*:
+ The simplest way to display remote images in UIKit is by using `NetworkImageView`. You need to provide the URL where the image is located and optionally configure a placeholder image that will be displayed if the download fails or the URL is `nil`. When there is no cached image for the given URL, and the download takes more than a specific time, the view performs a cross-fade transition between the placeholder and the result.
+ */
+
+class MyViewController: UIViewController {
+    override func loadView() {
+        let view = UIView()
+        view.backgroundColor = .systemBackground
+
+        let imageView = NetworkImageView()
+        imageView.url = URL(string: "https://picsum.photos/id/237/300/200")
+
+        imageView.translatesAutoresizingMaskIntoConstraints = false
+        view.addSubview(imageView)
+
+        NSLayoutConstraint.activate([
+            imageView.widthAnchor.constraint(equalToConstant: 300),
+            imageView.heightAnchor.constraint(equalToConstant: 200),
+            imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
+            imageView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
+        ])
+
+        self.view = view
+    }
+}
+
+//: [Next](@next)
+
+PlaygroundPage.current.liveView = MyViewController()

Playgrounds/NetworkImage.playground/Pages/Table_of_contents.xcplaygroundpage/Contents.swift

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+/*:
+ # NetworkImage
+ NetworkImage is a Swift µpackage that provides image downloading, caching, and displaying for your SwiftUI apps. It leverages the foundation URLCache, providing persistent and in-memory caches.
+
+ 1. [Displaying network images](Displaying_network_images)
+ 1. [Customizing network images](Customizing_network_images)
+ 1. [Creating custom network image styles](Creating_custom_network_image_styles)
+ 1. [Displaying network images in UIKit](Displaying_network_images_UIKit)
+ 1. [Using `ImageDownloader`](Using_Imagedownloader)
+ */

Playgrounds/NetworkImage.playground/Pages/Using_ImageDownloader.xcplaygroundpage/Contents.swift

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+//: [Previous](@previous)
+
+import Combine
+import PlaygroundSupport
+import UIKit
+
+import NetworkImage
+
+/*:
+ If you need a more customized behavior, like applying image transformations or providing custom animations, you can use the shared `ImageDownloader` object directly.
+ */
+
+class MyViewController: UIViewController {
+    private lazy var imageView = UIImageView()
+    private var cancellables: Set<AnyCancellable> = []
+
+    override func loadView() {
+        let view = UIView()
+        view.backgroundColor = .systemBackground
+
+        imageView.translatesAutoresizingMaskIntoConstraints = false
+        imageView.backgroundColor = .secondarySystemBackground
+        view.addSubview(imageView)
+
+        NSLayoutConstraint.activate([
+            imageView.widthAnchor.constraint(equalToConstant: 300),
+            imageView.heightAnchor.constraint(equalToConstant: 200),
+            imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
+            imageView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
+        ])
+
+        self.view = view
+    }
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+
+        ImageDownloader.shared.image(for: URL(string: "https://picsum.photos/id/237/300/200")!)
+            .map { image in
+                // tint the image with a yellow color
+                UIGraphicsImageRenderer(size: image.size).image { _ in
+                    image.draw(at: .zero)
+                    UIColor.systemYellow.setFill()
+                    UIRectFillUsingBlendMode(CGRect(origin: .zero, size: image.size), .multiply)
+                }
+            }
+            .replaceError(with: UIImage(systemName: "film")!)
+            .receive(on: DispatchQueue.main)
+            .sink(receiveValue: { [imageView] image in
+                imageView.image = image
+            })
+            .store(in: &cancellables)
+    }
+}
+
+//: [Next](@next)
+
+PlaygroundPage.current.liveView = MyViewController()

Playgrounds/NetworkImage.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='6.0' target-platform='ios' display-mode='raw' buildActiveScheme='true'>
+    <pages>
+        <page name='Table_of_contents'/>
+        <page name='Displaying_network_images'/>
+        <page name='Customizing_network_images'/>
+        <page name='Creating_custom_network_image_styles'/>
+        <page name='Displaying_network_images_UIKit'/>
+        <page name='Using_ImageDownloader'/>
+    </pages>
+</playground>