Updated File Types docmentation
Updated Contributing Documentation
Revert "Updated Contributing Documentation"
Checked in under wrong branch

This reverts commit 6634cb9df4b6f1ac9d0e2a4673be5ffe221e326b.
Updated contributing page
Updated Mastering Markdown

Removed coming soon sections -- Don't know if these are coming :)
Reviewed testing section to ensure it is consistent with testing changes
add missing list of changes, link to GitHub release notes