Added SHA512 for entry
Merge pull request #16 from matthiasbeyer/add-entry_hash

Added SHA512 for entry
Removed all old stuff from README
Implemented TagFilterCommand class
Reimplemented the Tagfilter filtering
Added Tree class with appropriate filter methods
Fixup: Added missing `end` kw for #filter in TagFilterCommand class
Added filter command comment
Added constructor for tag command class
Pulled filter helper methods one level up
Pulled the #filter_tree meth one lvl up, implemented CategoryFilterCommand