Add optional support sublime color scheme files via external crate

[Lepidopteran]

It's been a while for any movement on issue #244, So I've come here to discuss adding a optional dependency on sublime-color-scheme crate to add the ability to parse .sublime-color-scheme files to syntect.

Any feedback is greatly appreciated!

Resolves #244

Results

I've tested with a couple themes that use the sublime-color-scheme file format with great results taken from my comment on the issue:

Kanagawa

Catppuccin

Nord

Monokai

Gruvbox Material

[Lepidopteran]

Im not fully sure, if I did something wrong with the Build/Test Check