Separated Interpreter.sml into three separate files. The unification algorithm is in Unification.sml, the code for executing special built-in predicates is in SpecialPredicates.sml, and the interpreter logic is still in Interpreter.sml. Also tweaked the function signatures of special predicates to make them compatible with the compiler.
Added support for built-in predicates in compilation. Added automatic execution of queries when a compiled program is loaded.