BlockJoin improvements for Rails applications

[DougKeller]

Thanks for your PR - because this isn't part of the official branch yet, we chose to try out your changes for our Solr needs.

That said, there were a few changes/improvements we had to make to get it up and running for our app. Unfortunately these changes haven't been tested due to time constraints, but I wanted to put up this PR for you to consider some things that may have been missed.

Changes:

• Prevent indexing of a child doc without indexing its parent.
  • Because child/parent docs are expected to be indexed in sequence, indexing a child without its parent will break the index for that child/parent pair.
• Accept Rails collection proxies has a valid child_documents value
  • CollectionProxy instances are enumerable, so it'll behave the same as an Array
• Escape the parent filter values when performing a BlockJoinQuery.
  • Our models had colons in their class names due to being nested within modules. Not escaping these colons was causing solr query parsing issues.
• When performing a BlockJoin facet, only filter on the parent type
  • When the json facet was specifying the allParents filter to be the full all_parents_filter, facet values were coming back incorrectly. Changing this to only filter on type:parent fixed the counts.
• Fixed a bug with FieldJsonFacet not setting name correctly
• Implicitly include child documents in the query result when performing a BJQ
• If a hit returns _childDocuments_ in its field list, serialize each _childDocuments_ value as a Sunspot::Search::Hit
• Add support for sorting on child document fields
  • order_by :some_field, :desc, block_join: on_child(Child) { with(...) }

[DougKeller]

We ultimately ended up going a different route than BJQ for our app due to issues with keeping parent/child docs in sync, so I have deleted our fork of this branch. I'll still leave this PR open in case there's anything valuable in it, however it's unmaintained and isn't totally bug-free.

[giovannelli]

Hi @DougKeller thank you for the PR, we'll review it. I'm sure there some valuable stuff here.