Refactor commands

In fact, I have the one and only command. Also, prettify some strings.

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>
Use spec directory for testing

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>
Implement colour primitives

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>
Refactor RGB colour

Change lots of stuff. Add comments. Fix tests.
Add docs for HEX colour class

And fix a related test.
TERM: add custom #inspect (it's neat)
Add comments

And refactor #validate_attrs
TERM: Add YARD tags
Add support for 256 colours
Move Layer to its own file
Move ANSI to its own file
Add needed "require" statements

Also, remove `FG` from private constants
Move Effects to its own file
Color256: Use less space for effects methods

Maybe it's wankery, but still.
Remove old crufty testing APIs
Restructure some files

Add `Layered` and `Formatting` modules. Remove `ANSI` to `Color`. Make
some amendments, so tests for `Color256` can pass.
Remove old code and refactor version extraction
Remove test directory, since we use spec one now
Remove unwanted files
Require unrequired files