Added support for @code ... @endocde commands

[nikarh]

Adds support for doxygen code commands

Notable changes:

• Added \t char as a possible whitespace
• Whitespaces used to be collapsed in the lexer. Since code blocks should retain all formatting, lexer emits Whitespace items for every whitespace instead. Now they are collapsed in the parser, which checks if the last GrammarItem ends with a whitespace
• @code can optionally have an additional parameter (lang) passed with brackets as in @code{.py}. For that, I changed the parameter parsing logic to parse parameters separated with whitespace (including multiple whitespace lexemes) and inside of the brackets.

[Techie-Pi]

I'll try to review this PR in the weekend, thank you for your patience! :)

[pheki]

Hi! Any updates @Techie-Pi? We've been waiting on this for https://github.com/vita-rust/vitasdk-sys/pull/30

[Techie-Pi]

Sorry, I've not been able to review this PR sooner, lots of exams... I'll try to publish a new release in the following weeks. In the meantime you could depend on the repo itself.

[pheki]

No worries and TYSM!