Rename to mdx_superscript.py?

[heston]

Currently, it is not easy to add this module using pip and virtualenv, since the install path is very specific. Doing a pip install https://github.com/sgraber/markdown.superscript/tarball/master does not work because the module gets installed in site-packages. However, according to http://pythonhosted.org/Markdown/extensions/api.html#makeExtension, if you rename your module to "mdx_superscript.py" it will get loaded no matter where it is in the load path. This would also make it easier to install from PyPi (if you chose to go that route).