Pushes new meta data onto the stack - each meta represents a class being defined,
we operate a stack so that we can handle inner classes

@param className {String} name of the class being defined
function(className) {
      var pos = className.lastIndexOf("."); 
      var meta = {
          className: className,
          packageName: pos > -1 ? className.substring(0, pos) : null,
          name: pos > -1 ? className.substring(pos + 1) : className,
          superClass: null,
          interfaces: [],
          mixins: [],
          functionName: null
      };
      this.__metaStack.push(meta);
      this.__classMeta = meta;
      this.__metaDefinitions[className] = meta;
      this.__numClassesDefined++;
    }