Updated README

This is the code used in the Kelleher et al paper. This release is the same as 0.0.1, but the README is updated with regards to installation and usage considerations.

First official release

This release corresponds to the code used in the Kelleher et al. preprint.

It includes the simulation code functions used to run the C++ benchmarks in that paper.

The roadmap for future releases is:

1. Tracking mutation metadata.
2. Tracking ancestral samples + their metadata.
3. Solidifying the API on both the C++ and on the Python sides.

Once the above are accomplished, we anticipate rolling these features into fwdpy11 itself.