New Lexer

[ryankopf]

If you ever come back to this project, I want to note I am starting my own HAML parser and renderer. So far I have only made a new Lexer and have not done the parsing, but it's streamlined and handles both inline and multiline comments so far.

https://github.com/ryankopf/hamlrs

Happy to collaborate for a great, official Rust HAML parser!