stardate: Combining dating methods for better stellar ages

This is the release associated with the Journal of Open Source Software paper.

Changes:

Posterior samples are no longer saved to file by default.
Default number of walkers was increased to 50.
The SingleStarModel isochrones object is now used, rather than StarModel.
Improvements were made to tests and continuous integration was incorporated.
Added extinction (Av) as a keyword argument.

stardatev0.1.0

The first release of stardate.