[API] Change priority of attributes in merge
[Defaults] Fixed mapping of debug severity to str
[API] Added DECLARE_LOCAL_KEYWORD

It's usefull for declaring application-specific keywords which should be
written to file log
Merge pull request #24 from euroelessar/master

Several fixes in API and defaults.
[Code Style] Tiny renaming.
[Unit Testing] Added tests to check priority of categorized attribute sets.
[Aux] Added attribute name typedef.
[Aux] Scoped attributes now have less priority than local.
[Code Style] Style.
[Version] Bump.
[Aux] Added changelog files to the tracking system.