Obtain dependencies automatically.

I switched from distutils to setuptools. Now, running `python setup.py
install` automatically gets the dependencies from PyPi. I also edited
how the dependencies were listed in setup.py.

Previously, running `pip install cvxpy` did NOT get the dependencies.
Now, if a new release is created for cvxpy, `pip install cvxpy` should
automatically get the dependencies.

Should allow us to close #34.