Added md::Class and md::SemanticError, updated CMakeLists, Namespace and Scope accordingly
Added new attributes to md::Class;
Implemented parser::BaseSpecifier class to represent the specification of a base class for a class;
Implemented grammar rules and corresponding types and semantic code for Classes;
Changed grammar NamespaceAction to ScopeAction;
[opwig] made some small changes to md::Class and parser::BaseSpecifier;
[opwig] implemented some unit tests for md::Class and parser::BaseSpecifier;
[opwig] 'fixed' anonymous class declarations (it does not gives other classes trouble, however it wont work);
[opwig] implemented a few more unit tests for Class metadata;
[opwig] implemented more md::Class unit tests;
Merge branch 'mdclass' into declaration