Support Markdown Profiles

[ghost]

The test tool has been great at getting my new profiles set-up. My only nit is that it requires my speedtracker profiles to use .html as a file extension (whereas I'd prefer to use .md or .markdown. I know I left some related comments in the speedtracker repo, but this issue is specifically to discuss the 404 returned by the test tool when a profile collection item uses one of the several valid Jekyll formats, and what kind of support is desired WRT to providing an experience which allows individuals to use other file extensions.