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/consts.go

@@ -79,10 +79,15 @@ var (
 		mediaJSON: json.MarshalIndent,
 		mediaXML:  xml.MarshalIndent,
 	}
+	// valid MIMEs.
 	okAcceptMime []string = []string{
 		mediaJSON,
 		mediaXML,
 		mediaYAML,
 		mediaHTML,
 	}
+	// These are actually HTML.
+	htmlOverride map[string]bool = map[string]bool{
+		"Links": true,
+	}
 )