Epsie

Summary:
* Drop possibility to update proposal before jump.

* Added support for Python 3.6. May also work on other 3.x versions, but I haven't tested it yet.
* Added ability to checkpoint to HDF5 files.
* Added ability to update proposals both before and after a jump.
* Fix a bug in the way temperature swaps and acceptance ratios were being saved.
* Fix various other bugs and typos.

This version includes a Metropolis-Hastings sampler and a parallel tempered sampler.