FIXES:
* There was an edge case where a raw body for HTML would potentially
result in a nil byte slice exception. This has been fixed.
(I don't even know if it was possible, I just made sure it wasn't.)
* The links browser is now explicitly returned as HTML and properly
detected as a "browser".
* Hyperlinks for links, w3m added to Usage page.
* Content-Type is now always set correctly; there were cases where it
was improperly returning e.g. text/plain for JSON.