Pre-release alpha version of emcee

This should be feature parity with the `python` version, for features
that are central to the `emcee` Ensemble Sampler. For info about which
features are included in the "partity" milestone, see the [milestone list](https://github.com/mindriot101/rust-emcee/milestone/1)

* Optionally disabling storing of the chains [#6](#6)
* Add ability to thin the resulting chain [#4](#4)
* Speed up compilation by not depending on [`error-chain`](https://crates.io/crates/error-chain)
* Use `f64` by default for improved precision
* Add ability to restart the sampler from a known position [#3](#3)

emcee version 0.3.0

* This includes iterative sampling, using a closure.

See the
[`sample`](https://docs.rs/emcee/0.3.0/emcee/struct.EnsembleSampler.html#method.sample)
documentation.

emcee v0.2.0

* Include multivariate sampling test

Initially, when this test was implemented it highlighted that the
sampling was incorrect. With the implementation of this test comes
correct behaviour for the sampling.

This change is therefore worth a version bump even though there is only
one change in this new version.

v0.1.1

Improve crate documentation

Initial release to the public