Add comment about changing defaults

I think this satisfies the problems detailed in pull #171, namely
these are "constants" created at module-load time, are internal,
aren't part of the API and thus shouldn't be changed by people
using ElasticUtils.
Test for caching empty results
Cache empty results
Added support for filter and query facets.
Merge pull request #174 from jezdez/more-facets

Added support for filter and query facets.
Added tests for filter and query facets.
Added docs for filter and query facets.
Merge pull request #175 from jezdez/more-facets

Added tests for filter and query facets.
Merge pull request #173 from infoxchange/cache-empty-results

Empty results from ES not cached
[Doc] Indexing examples lacking `properties` key when configuring mappings.

The code examples for setting up mappings using both `create_index` and `put_mapping` don't include the properties key in the dict provided.
Merge pull request #177 from catalanojuan/patch-1

[Doc] Fixed: Indexing examples lack the `properties` key when configuring mappings
Migrated to elasticsearch-py, the official ES client

this should provide more compatibility going forwards as well as
performance boost.
Patch fixes, thanks @robhudson!
Updated docs to use elastisearch-py
By default connect to localhost, not localhost:9200

9200 is http port that would break if thrift was requested for example
Forgotten 'when' in docs, thanks robhudson!
Update CHANGELOG re: elasticsearch-py
Update CONTRIBUTORS file