Use setuptools entrypoints instead of scripts/nikola

This makes us a bit more “hip”, “cool” and “modern” (and I love making us more like that and use more setuptools magic).  According to the [setuptools docs](http://pythonhosted.org/setuptools/setuptools.html#automatic-script-creation):

> On Windows, a .exe launchers are created, alongside a .py files. The .exe wrappers find and execute the right version of Python to run the .py or .pyw file.

So, one more problem handled nicely (I hope.)

@ralsina, general opinions, ideas, suggestions?  Is this sane or should this be dropped?