refactored keywords
[[ RefactorSyntax ]] Finished refactoring keywords.
Merge branch 'refactor-syntax_unicode_shims' into refactor-syntax_unicode_property_keywords
[[ RefactorSyntax ]] Switched to using refactored MCComref / MCFuncref.
[[ RefactorSyntax ]] Moved keywords exec methods to their own file.
[[ RefactorSyntax ]] Changed MCConstant and MCLiteral* to use eval_ctxt.
[[ RefactorSyntax ]] Changed ES_EXIT_SWITCH case in execute commands back to return ES_NORMAL.
Merge branch 'refactor-syntax_unicode_shims' into refactor-syntax_unicode_property_keywords
Udpated Makefile to include exec-keywords.cpp in compilation process