Remove stemming override for 'permitting'

Environment Agency prefer ‘environmental permit’ and ‘environmental
permitting’ to be interchangeable
Synonym updates following unified search and best bets

Remove synonyms that are no longer needed with recent weighting
improvements or can now be handled better through best bets; also
reinstate a couple that were causing problems in the past
Analyze the specialist_sectors field

We were originally not analyzing the specialist_sectors field because we
had a plan to move to storing this in an internal tags field.  However,
we don't currently have any searches which require a single internal
tags field, so this is probably a misstep for now.  Changing the field
to be analyzed will make it available for searches after we next run a
deploy:migrations.

Also, don't allow use of the tags field in searches, since it shouldn't
be visible externally.
Merge pull request #256 from alphagov/synonyms-20140714

Synonym updates following unified search and best bets
Tidy up, remove old constants
Merge pull request #257 from alphagov/remove_old_constants

Remove old constants, make some things private
Expand specialist_sectors field

The specialist sectors aren't yet being indexed, but when they are this
will the specialist_sectors field in search results.

The main reason for implementing this now is that we also want to store
example values in the SpecialistSectorsRegistry, so we need to create
that object first.
Support stubbing the metasearch index

Also, memoize the index stubs so that repeated calls to them within a
test return the same stub.
Functional test for sector expansion
Merge pull request #252 from alphagov/expand_specialist_sectors

Expand specialist sectors

https://www.pivotaltracker.com/story/show/73972778
Add dependencies to README
Add hash_including test helper

Because RSpec is better
Add support for document_type filter

Allow filtering by elasticsearch's _type field. This will be used for
finder-frontend.
Add AAIB Reports schema

In order to expose AAIB reports in search, we've added the schema for
the facets on the reports.

Trello ticket:
https://trello.com/c/X4vUOJzE/203-add-aaib-reports-into-search-results-2
Merge pull request #258 from alphagov/document-type-scope

Add support for document_type filter
Merge pull request #259 from alphagov/add-aaib-reports-schema

Add AAIB Reports schema
Allow extra options to be supplied for faceting

We want to allow callers to request that a set of example documents are
returned when faceting.  As a first step towards this, this commit
changes the facet parameters to accept a set of additional
comma-separated facet parameters; within each facet parameter, keys and
values are separated by colons.  For example:

    facet_organisations=10,examples:5,example_fields:link:title,example_scope:global

The parameters will actually be used by subsequent commits.
Add Index.msearch method for multiple searches

This accesses the _msearch endpoint in Elasticsearch to allow lots of
queries to be run concurrently.  Useful for doing lots of individual
lookups.
Replace unused iteration parameter name with _
Fetch facet example values when requested

Uses the msearch API to perform a query for examples for each facet
example in parallel.