Add ExDoc for documentation

This change adds ExDoc as the documentation tool for the project.

mix.exs

@@ -26,7 +26,8 @@ defmodule BambooPostmark.Mixfile do
      {:hackney, "~> 1.6"},
      {:poison, ">= 1.5.0"},
      {:plug, "~> 1.0"},
-     {:cowboy, "~> 1.0", only: [:test, :dev]}]
+     {:cowboy, "~> 1.0", only: [:test, :dev]},
+     {:ex_doc, "~> 0.13", only: :dev}]
   end
 
   defp package do

mix.lock

@@ -2,6 +2,8 @@
   "certifi": {:hex, :certifi, "0.4.0", "a7966efb868b179023618d29a407548f70c52466bf1849b9e8ebd0e34b7ea11f", [:rebar3], []},
   "cowboy": {:hex, :cowboy, "1.0.4", "a324a8df9f2316c833a470d918aaf73ae894278b8aa6226ce7a9bf699388f878", [:rebar, :make], [{:cowlib, "~> 1.0.0", [hex: :cowlib, optional: false]}, {:ranch, "~> 1.0", [hex: :ranch, optional: false]}]},
   "cowlib": {:hex, :cowlib, "1.0.2", "9d769a1d062c9c3ac753096f868ca121e2730b9a377de23dec0f7e08b1df84ee", [:make], []},
+  "earmark": {:hex, :earmark, "1.0.1", "2c2cd903bfdc3de3f189bd9a8d4569a075b88a8981ded9a0d95672f6e2b63141", [:mix], []},
+  "ex_doc": {:hex, :ex_doc, "0.13.0", "aa2f8fe4c6136a2f7cfc0a7e06805f82530e91df00e2bff4b4362002b43ada65", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, optional: false]}]},
   "hackney": {:hex, :hackney, "1.6.1", "ddd22d42db2b50e6a155439c8811b8f6df61a4395de10509714ad2751c6da817", [:rebar3], [{:certifi, "0.4.0", [hex: :certifi, optional: false]}, {:idna, "1.2.0", [hex: :idna, optional: false]}, {:metrics, "1.0.1", [hex: :metrics, optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, optional: false]}, {:ssl_verify_fun, "1.1.0", [hex: :ssl_verify_fun, optional: false]}]},
   "httpoison": {:hex, :httpoison, "0.9.1", "6c2b4eaf2588a6f3ef29663d28c992531ca3f0bc832a97e0359bc822978e1c5d", [:mix], [{:hackney, "~> 1.6.0", [hex: :hackney, optional: false]}]},
   "idna": {:hex, :idna, "1.2.0", "ac62ee99da068f43c50dc69acf700e03a62a348360126260e87f2b54eced86b2", [:rebar3], []},