setup.py improvements (develop)

Here's a new ``setup.py``. The improvements include: 
* Requires (and installs) numpy, pandas, and pytz
* Compiles the cython spa code.
* Follows common setup.py patterns.

I tested this in a clean virtual environment with only python 2.7.8, setuptools, and pip (from virtualenvwrapper). Cloning my repo, checking out the develop-setuptools branch, and then running ``pip install .`` worked for me. I'm expecting that other users will find some problems.

I based this on be1b140. I think that this PR and #28 can be completed in any order. I can rebase if there's a problem.