Convert Wiki markup to Pivotal/Github-flavored Markdown

[ghidinelli]

Thanks for your script, I used it as the basis for a Trac/Postgres migration. I also borrowed/cleaned up some code to migrate more of the Wiki syntax so headers/etc would work properly. Here's a gist if you feel like enhancing it:

https://gist.github.com/ghidinelli/9e84209c09997f2b938c