Chainable filter set
Pass filterSet as second arg to filter callback
Expose root object at `_root_` property
Inheritance friendly set items.

Finally set items work cross prototype chains.
item.value no longer returns subject value of item but true/false value that represents whether value is set on set or not.
item.subject returns value that is subject of a set
Live property name-sets with optional tag filters

Removed old getPropertyNames implementation