Rework literals

[dvanhorn]

Should adopt the Mountebank AST approach early on and have (Quote <datum>) where <datum> is just integer to begin, then add boolean, char, etc. Mountebank would then just add pairs, vectors, etc.

Rework pattern matching to eliminate a bunch of pattern forms and pun expression forms, eg. (PVar x) is just (Var x) and (PLit d) is just (Quote d). Have to revisit after Mountebank.