cannot pip install

because of our convoluted installation script, there are packages that a user must have installed before they can pip-install wetb.

in particular: future, numpy, and cython are required, and pypandoc is desired but not required.

either we fix our installation script (MAJOR BONUS POINTS FOR A CYTHON-FREE VERSION) or we update our installation instructions.

also one of our tests should verify that wetb can install cleanly.

cc @mikf @mmpe