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