API for a clean conversion from wikitext to parsoid-format HTML.

Just add 'format=html' to the parameters on your POST if you don't
want the textarea, etc in the response.

Change-Id: I49a3abb34e5c4ccbcfc3e7b41684b8d9adbc1c18
Merge "API for a clean conversion from wikitext to parsoid-format HTML."