Support Rust Language

[zufuliu]

[zufuliu]

Related issues:

• Add Rust syntax highlighting XhmikosR/notepad2-mod#126
• Need syntax highlighting support for Rust rizonesoft/Notepad3#509

[zufuliu]

The Rust Programming Language
https://doc.rust-lang.org/book/
https://doc.rust-lang.org/reference/index.html

[zufuliu]

Lexer for Rust and API list for Rust standard library (except for platform-specific extensions) is added in c37abf4 and 63e4f82.