2 Dimensional Routed Aliases

Current available routed aliases are restricted to a single field. This feature will allow Solr to provide data driven collection access, creation and management based on multiple fields in a document. The collections will be queried and updated in a unified manner via an alias. Current routing is restricted to the values of a single field. The particularly useful combination at this time will be Category X Time routing but Category X Category may also be useful. More importantly, if additional routing schemes are created in the future (either as contributions or as custom code by users) combination among these should be supported. 

It is expected that not all combinations will be useful, and that determination of usefulness I expect to leave up to the user. Some Routing schemes may need to be limited to be the leaf/last routing scheme for technical reasons, though I'm not entirely convinced of that yet. If so, a flag will be added to the RoutedAlias interface.

Initial desire is to support two levels, though if arbitrary levels can be supported easily that will be done.

This could also have been called CompositeRoutedAlias, but that creates a TLA clash with CategoryRoutedAlias.