Add run_tests.py to setup Django for testing.

This will set up the Django environment so the Django-specific tests can
run. If Django is not present, the setup will be skipped and the tests
will be run normally. The testsuite will skip any Django-specific tests
in this case. This simplifies running the full test suite.
Merge pull request #91 from mythmon/run-tests-helper

Add run_tests.py to setup Django for testing.
Fix test errors if django is not installed

If django is not installed, then we don't import get_es and then this
code fails. But we don't need the get_es method on QueryTest anyhow,
so this nixes it.
Implement prefix filter support
Add Mike to CONTRIBUTORS
Tweak sample_facets.py

* clarifies some of the comments
* adds a `.es()` chainable to the S so if someone changes the HOST,
  it's looking at the right place
Issue #89. Added note that EU doesn't work with ES 0.19.9.

The problem is this one:

https://github.com/elasticsearch/elasticsearch/issues/2205

This was a bug in ElasticSearch 0.19.9 that was fixed in 0.19.10 so
I added a note to the docs stating ElasticUtils doesn't work with
ElasticSearch 0.19.9.
Prep for 0.6 release
Tweak formatting in CHANGELOG
Update version to v0.7.dev
Massive update to pyelasticsearch

* nix pyes things
* update to pyelasticsearch things
* fixes MLT so it works with pyelasticsearch (requires fixes that
  should be in pyelasticsearch 0.3 when that gets released)
* changes MLT fields argument to mlt_fields
* nixes all the dump curl code
* cleans up imports
* fixes defaults so that S defaults to searching all indexes and
  all doctypes
* adjusts errors so they all derive from ElasticUtilsError
* cleans up get_es() and S.get_es() so they're correct
* add DeprecationWarning for deprecated things
* update test code for MLT

In elasticutils.contrib.django:

* ditch the thread-local caching of ElasticSearch objects (we'll
  implement something better soon since pyelasticsearch's ElasticSearch
  objects are thread-safe)
* removed statsd code from the django-related code
* change ES_HOSTS to ES_URLS
* update index method (need to add a new bulk_index method)
* update test code for django-related bits
Update sample_facets.py to new API

This updates it to the new API, uses pyelasticsearch, and tweaks
some of the comments.
Update requirements

We require at least pyelasticsearch 0.3, but it's not out, yet.
Massive docs overhaul
Add bulk_indexing support to Indexable with tests
Nix max_retries; add ElasticSearch caching

* nixed max_retries because I personally think it's got a confusing
  name and, like revival_delay, it's probably not something someone is
  going to use often
* added caching of ElasticSearch object creation with tests
Nix todo, add docs for bulk_index, fix requirements
Tweak django tests to skip better

If django isn't installed, we want all the django tests to get skipped.
This fixes an issue with get_es not existing because it doesn't get
imported because django isn't installed.
Add link to pyelasticsearch docs
Fix Indexable.refresh_index and es args

pyelasticsearch refresh doesn't take a timeout, so nixing that.

Additionally, it's more flexible if Indexable had its own get_es()
class method that it defaults to using that can be easily overridden.
So I tweaked that code a little.