render long_description from markdown

@twobraids r?

What this does is that it converts the markdown text to reStructuredText when you run `python setup.py sdist` so that the long_description in the `PKG-INFO` file is in rst format. 

I like using Markdown because it's more important, to me, how the README looks on github than it does on pypi. However, pypi does not support Markdown and it's not simply a matter of looking at the extension of the readme file because what really matters is the `long_description` value sent to the `setup()` function and at that point it looses the `.md` extension stuff. 

There's a caveat here though. You have to install `pypandoc` and `pandoc` yourself on the machine you're building the sdist from. All `pypandoc` does is that it calls on, on the command line, to `pandoc`. 
Basically, if the person who runs the `python setup.py sdist upload` doesn't have those things installed, the pypi README will look a bit odd but it won't look any worse than it does today.