Eliminate non-namespaced class, standardizing on Xmf\Highlighter

Only consumer of Xoops_Highlighter was in Publisher module.
Move Xoops_Registry to proper namespace

- simplify new Registry class
- eliminate static declarations (all existing consumers use instance from $xoops->registry()
- simplify calls
- fix tests, some psr-2 cleanup, remove unused directory in Xoops
Fix documentation of register()
Merge pull request #221 from geekwright/nsconv1

Namespace cleanup Highlighter and Registry