Created ParserEvaluator.hs

Unified the two files to remove circular inheritance
Created stdlib.scm

A library of basic scheme functions
Modified ParserEvaluator.hs, REPL.hs, stdlib.scm

Added support for inter-type arithmetic, added autoloading of
stdlib.scm to REPL
Deleted Evaluator.hs, Parser.hs

Should have done this a while ago.  They stopped being necessary