MarkdownSharp Updates

These are some improvements to MarkdownSharp.

First I merged in latest improvements from the MarkdownSharp repo.  This seemed to only have a few smaller improvements... nothing major I could see.

Next I removed requirement for a blank line before lists and fenced code blocks.  This now matches GitHub markdown behavior.

Finally i used the same hash and restore technique they do for embedded HTML on fenced code blocks.  This fixes the case where a code block contained a line that begins with a `#` and it would convert it to a `<h1>` tag.