Support classes without param.pp defined

Also fix small issue with undefined exception
Improved hooks
Improve hook definition
Adding tests for new hooking features
More hooks examples in README
Various refactorings related to hooks
Fixes related for hooks and param-less classes
Merge pull request #76 from ares/fixes

Fixes and improved hooks
Bump version to 0.5.0
Automatic commit of package [rubygem-kafo] minor release [0.5.0-1].