Initial Gleam support

[aognio]

• Initial support for the Gleam programming language (gleam.run)
• Based on grammar rules from https://github.com/gleam-lang/tree-sitter-gleam
• Also tried to improve the lexer taking some bits from https://github.com/gleam-lang/gleam-highlight.js/blob/main/index.js

Here's an screenshot of how it looks:

We can compare this output to the same file on Github here:

https://github.com/gleam-lang/example-todomvc/blob/main/src/todomvc.gleam

[tancnle]

@aognio This would be better to be done as a plug-in than being bundled in Rouge core. It looks like Gleam is also implemented via highlight.js plugin.

[jneen]

Actually I wouldn't mind having Gleam in core. This lexer would have to be rebased and updated to pass the latest style checks though.