BUGFIX: Content-Type, Nil Raw Body Edge Case, Links

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.

server/tpl/usage.html.tpl

@@ -46,8 +46,8 @@ Accept: text/html
 						</pre>
 					</p>
 
-					Note that <a href="https://lynx.invisible-island.net/">Lynx</a> and <a href="http://elinks.or.cz/">Elinks</a> are considered "graphical"
-					browsers by this program as they are HTML-centric.
+					Note that <a href="http://links.twibright.com/">Links</a>a>, <a href="https://lynx.invisible-island.net/">Lynx</a>, <a href="http://elinks.or.cz/">Elinks</a>,
+					and <a href="https://w3m.sourceforge.net/">W3M</a> are considered "graphical" browsers by this program as they are HTML-centric.
 				</p>
 				<p id="usage_params_mod">
 					The following parameters control/modify behavior.<a href="#usage_params_mod">{{ $linkico }}</a>