Add Meson Lexer

[funatsufumiya]

This adds a lexer for Meson (https://mesonbuild.com/Syntax.html)

[tancnle]

Thank you for your contribution @funatsufumiya ❤️ And welcome to Rouge. The PR looks good to be overall. I have left some suggestions for your consideration.

In addition, could you kindly:

1. add some specs for this lexer, mostly around guessing (see Python spec for inspiration)
2. rebase this branch off master and add an entry to the Languages.md

Please let me know what you think 🙏🏼

[tancnle]

suggestion: Do you think we could consider specifying a mimetype as well?

mimetypes 'text/x-meson'

[tancnle]

thought (non-blocking): Since this inner-class is shared with the one in the Python lexer, I would suggest extracting this to a common place to reduce duplication. No action is required in this PR. I will take point on the follow-up PR.

[funatsufumiya]

@tancnle
Thank you. All suggestions might be cool, but I don't have enough time to achieve them quickly. I'll look through little by little.

[tancnle]

@tancnle Thank you. All suggestions might be cool, but I don't have enough time to achieve them quickly. I'll look through little by little.

No worries @funatsufumiya. In the spirit of iteration, let's merge this change for now 🚀 I can have a look at implementing them or you might beat me into it :)