(#174) Added original Markdown files back in

- Due to issues after StyleCop and FxCop'ing the Markdown.cs and TextToFlowDocumentConverter.cs files, adding originals back in
- Have marked them as auto-generated and GeneratedCode so that both StyleCop and FxCop ignore them
Merge pull request #178 from gep13/feature/Issue-174

Added original Markdown files back in