Remove lookahead clauses in LITERAL

[inaimathi]

• Introduce new
• Use CHAR+ instead of lookahead regex
• Add preprocess-block step to collapse resulting character sequences
• Call preprocess-block in parse-howl-file
• Add test2.howl to the testing resources (Not sure if we'll want to write smoke-tests using this parse-a-file approach, or if it would be better to write generators. Leaning towards the latter, but still isolating this snippet)

[jamesaoverton]

This looks good. I'll comment on a few lines (I haven't used that GitHub feature before).