Nix pyes

This is a big set of changes that fall into a few categories:

1. Ditches pyes for pyelasticsearch. In the process of doing that, I cleaned up a bunch of code that was goofy to get around pyes API funkiness (*cough*default_indexes*cough*). I also ditched some code that seems out of scope for ElasticUtils. The CHANGELOG should cover the details. I tested updating Fjord to use this and it took 30 minutes and the changes were pretty minimal.

2. Overhauls the documentation. This covers stuff that wasn't obvious before like slices, `.indexes`, `.doctypes`, ...

3. Updates the tests.

4. Fixes some other issues: adds prefix filter support, changes S defaults for indexes and doctypes (if you don't specify either, S searches everything now), etc.

Can I get some help looking this over? Best to start with reading the CHANGELOG to see what's changed, then probably reading through the docs, then looking at the code changes.