[opwig] implemented enum grammar rules (without semantic value yet)
[opwig] implemented Enum metadata object
[opwig] Implemented semantic action for Enum rules;
Implemented support for Enums in Scope;
Added newer grammar rule files to CMake file list;
[opwig] Implemented Enum unit tests;
Fixed a small bug in the grammar;
[opwig] Updated Enum metadata so that it can only have one base which is a primitive type;
Updated metadata, grammar rules and tests accordingly;
Merge branch 'enumspecifier' into dev