Semantic plugin: handling access specifiers
Semantic plugin: global refactoring, basic namespace handling

Changes:
 * Type attributes formatter refactoring.
 * Value of :type attribute in tag that refers to other tag is always "class" now.
 * Handlers for namespaces and using declarations & directives.

Todo:
 * Namespace- and class- qualified symbols are not fully supported yet.
 * Using declarations in classes are not supported yet.