Begin refactoring util to support facets.
Comment and import clean-up.
Pep 8 & Cleanup
Clean up pager.
Return facets and clean up facets generating code.
Further refactor the query functions for entities 
and relations.
Adapt relations filters to what the entities filter 
signature looks like.
Non-working: begin recursive facets.
Simple facets are now working, refs #54.
Refactor how properties are serialized by default.
Split up ‘util’ into ‘filters’ and ‘facets’.
Clean up facets code a but.
Comments.
Factor out apply facet call to ready for more 
specific group sets.
Support properly faceting properties.
Pager: cleaner name handling; option to pass
results function to constructor.
Support serializing generators to JSON.
Facets are returned as a pager now.
Fix up tests to reflect refactored method signatures.
Relations facets. Fixes #54.