Fix #98: Implement Rust highlighting support

[alopatindev]

No description provided.

[MightyCreak]

Hey @alopatindev !

What's the status on your PR ?

[alopatindev]

Thanks for noticing the PR!

It works for non-exotic code. Lifetimes highlighting is not implemented yet. I hope I'll make more progress soon.

[alopatindev]

Multiline strings, macros, character literals are also unimplemented.

I'll appreciate any help. I updated #98 with source code example.

[MightyCreak]

I did a pass and added support for various comments, chars and strings syntaxes.

Since the Rust language is becoming more and more used lately, I think I'll push it as is, even if it's not feature-complete, and hope that the community will jump in to fix the different issues.

Also, it would be interesting to see if a more modern GTK widget (like the one used in GNOME Builder) could bring syntax colorization without us having to create a syntax config for each language out there.