Renamed restriction methods, added where restrictions interface

- Renamed andt, andd, ande...., wheret, whered, ....
- Added interface for where restrictions, which is also implemented by the restrictionsgroup to allow more natural looking chaining (group.where(name).eq.... instead of group.and(..).eq)
Merge pull request #2 from gert-wijns/RestrictionsAPIRename

Renamed restriction methods, added where restrictions interface