Consider relaxing literals

[ErisDS]

Currently a literal is defined as:

Any character string which follows these rules:
- Cannot start with - or : but may contain them
- Cannot contain any of these symbols: '"+,()><=[] unless they are escaped
- Cannot contain whitespace

• reconsider not allowing : at the start
• reconsider if non-quote symbols can be allowed inside, but not at the start/end without escaping
• reconsider whitespace

When reconsidering we must:

• look for valid use cases
• write lots of tests in both the lexer and parser