Support for fenced code blocks for the MarkdownTextBlock XAML Control
In GitHub Flavored Markdown (GFM), you can create code blocks using triple backticks (```, see https://help.github.com/articles/creating-and-highlighting-code-blocks/)
While asking for syntax highlighting may be a bit too much at this point, basic support for the triple backtick syntax would be nice. The GFM language specifier behind the backticks could be ignored in the first iteration.
Done in 1.4