split the parser into a lexer/parser

[cdepillabout]

I think it would be a little easier to change the parsing code if it was split into a lexer/parser (like most programming languages).

I'm going to add the help-wanted label, but I plan on doing this myself when I get the time.

[cdepillabout]

I left this as a comment on #9, but I think it is worth posting here as well:

It is possible that all we really need is a lexer, and not a lexer/parser. It might be possible to figure out the output indentation and color based entirely on lexed input instead of fully parsed input.

[andrew-lei]

Should this be closed?

[cdepillabout]

Yes, thanks a lot!

This was implemented by @andrew-lei in #37!