First beta release

A first beta release for pyfrost.

Changes since alpha:

• Huge refactor of underlying C++ code, instead of emulating a complete NetworkX DiGraph class, we now emulate three internal dicts. The BifrostDiGraph is now a proper subclass of networkx.DiGraph, and many more functions and algorithms of NetworkX work out of the box.
• A big benefit of above refactor is support for NetworkX's subgraph views
• Iterating over a Bifrost graph's nodes now includes both the forward and reverse strand.

v0.1.2-alpha

Add pybind11 dependency

Alpha release

This is a pre-release, still in heavy development and bugs. Created a release tarball to make it installable with pip.

v0.1.0a3

Fix setup.py pybind11 dependency