Derive Hash for more style types

[markus-bauer]

Color derives Hash:

crossterm/src/style/types/color.rs

Lines 30 to 31 in 4549831

	#[derive(Copy, Clone, Debug, PartialEq, Eq, Ord, PartialOrd, Hash)]
	pub enum Color {

But most others don't:

crossterm/src/style/types/colors.rs

Lines 29 to 30 in 4549831

	#[derive(Debug, Clone, Copy, PartialEq, Eq)]
	pub struct Colors {

crossterm/src/style/attributes.rs

Lines 6 to 7 in 4549831

	#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
	pub struct Attributes(u32);

...etc.

Can you add this, or is this by design?

[joshka]

Seems like a reasonable thing to add. Can you submit a PR?