add favicon for site

* Fixes #177
* Note that this doesn't seem to work (for me) in vagrant on localhost --- i think browsers don't want to load a favicon for localhost:8080.  And firefox is very slow to come to the conclusion that it needs to look for a favicon again.  However, pushing it out to pagoda and trying in Safari, i got the favicon to appear, so that means it works, and it's just a matter of time until firefox will load it.