Added content to the evaluation and conclusion chapters.
Minor bugfixes.
Compiled code can now be made to print out a simple trace during execution.
Altered the parsing grammar to handle unary minus
Old, uncommitted changes to interpeter, from when code was moved to be shared with the compiler.
Updated the special predicates to handle unary minus terms.
Removed the separate implementation of 'greater-than', changed it into a call to 'less-than' with reversed args.