Markdown: Fix HTMLX buffers

Use actual IContentType within ProjectionBuffers.
Warning: Extremely unreliable.

In particular, this breaks ProjectionBufferHelper.GetHtmlBuffer(),
which also assumes that there is only one HTMLX buffer.
This kills the parent buffer's ContainedLanguage support partway
through.

Separately, editing in the embedded buffer is very unreliable.
Analysis: (CA1702) Compound words cased correctly.
Analysis: (CA1030) Use events where appropriate.
Analysis: (CA1063) Implement IDisposable correctly.
Fixed #266 by standardizing ignore folders
Fixed Markdown compiler issues
v1,4
Cleanup: Code formatting.