Parsedown tests

The parsedown library has a huge set of tests, and I've quite literally stolen them. 

I'll work out where and how to put attribution where at some point, but for now we have their markdown example files.

I wrote a bit of Node JavaScript (I feel dirty and im on a plane so I cant shower) to convert all of the original Parsedown files into the HTML that a compliant CommonMark implementation would expect.

There is a broken one for now, and code might need to be moved around, but I wanted people to take a look and see what they think.