remove numpy bootstrap hack in setup.py

[jairideout]

This hack causes #997, which doesn't have a clear/clean fix. Since we're moving forward with conda, which doesn't have this problem, I think we should remove the hack and acknowledge that when installing scikit-bio with pip/setup.py, numpy must be installed first.

Update README.rst pip install instructions to be:

pip install numpy
pip install scikit-bio

[souravsingh]

I would like to work on the issue

[ebolyen]

Sounds great, thanks @souravsingh!