Improve term! macro to support extra prolog syntax

[matko]

As per #4, currently the term! macro does not support

• quote notation for atoms
• cons-list notation (useful for unification with tails)
• dynamic functor names (useful for runtime predicate definitions)

This should be improved.

[ThePuzzlemaker]

Another useful addition could be the neck operator :-, conjunction ,, etc. The neck can just be turned into a term as the functor application :-(Head, Body) where Head is a functor before the neck and and Body is the part after. Conjunction is similar, iirc
Though this would probably mean making a full-fledged precedence parser.

[ThePuzzlemaker]

(At that point it may be helpful to consider trying to leverage PL_chars_to_term, perhaps? Then we could replace all unquotes (#foo) as variables then find those variables and unify with the terms)