Category attributes and their properties for indexing

Attributes for a category, possibly containing category property's.

Interface Summary
Interface	Description
CategoryAttribute	An attribute which contains for a certain category the `CategoryPath` and additional properties.
CategoryProperty	Property that can be added to `CategoryAttribute`s during indexing.

Class Summary
Class	Description
CategoryAttributeImpl	An implementation of `CategoryAttribute`.
CategoryAttributesIterable	This class transforms an `Iterable` of `CategoryPath` objects into an `Iterable` of `CategoryAttribute` objects, which can be used to construct a `CategoryAttributesStream`.
OrdinalProperty	A `CategoryProperty` holding the ordinal from the taxonomy of the current category in `CategoryAttribute`.

Package org.apache.lucene.facet.index.attributes