Simdna

Corresponds to PR https://github.com/kundajelab/simdna/pull/10 by hannahgz

To get deterministic results, only have to set the seed in `simdna.random` (as opposed to setting the seed in both `np.random` and `simdna.random`). `simdna.random` is now a numpy RandomState object augmented with a `random()` function to meet the api of the python `random` module as well as the `np.random` module.

This version patches v0.2 with a custom random number generator to ensure reproducibility in IPython/Jupyter notebooks.

Tagged for dragonn 0.1.2. Includes bugfix for partial overwriting of motifs.

Initial pre-release for integration with dragonn.