Fix CssSmartTagger disposal
Fix trans-buffer boundaries

Add a newline between the texts of each buffer.
This newline will become part of the underlying
text seen by the "foreign" language service; it
will never be displayed in the editor.
Register Markdown files with HtmlEditorFactory

Fixes IntelliSense, ProjectionBuffers, and more...
Revert "Try to expose IWebEditorFactory for Markdown"

This reverts commit 228da85eeb38f40894797ebafc3416d86d62e577.
This is alleviated by 3027ff9fc4c89668b7c0dad7c8967431c836007e