Feature: Add syntax highlighting

[mahdix]

No description provided.

[titpetric]

Did consider adding this from the start, but matching the scroll % from the left pane was very hard, because either the editors I considered didn't have a function that would set the scroll offset, or didn't make it easy to add/get it from their APIs. It's not a good first issue for somebody to tackle, but it would be nice to have.