Add support for multi-line and other comments

Currently the S-expression lexer and parser only support comments that start with ";". However Racket and other Scheme variants also support more types of comments, a notable one is the multi-line comment that starts with `#|`.

Other types of comments supported in Racket:
https://docs.racket-lang.org/reference/reader.html#%28part._parse-comment%29 (1.3.9 Reading Comments). 
