file monitoring on OSX + minor changes

Hi Steven,

First, let me say, very exciting project!

inotify isn't available on OSX, so I added support for fsevent.  For future reference, I later discovered Listen, which looks like it might be the preferred way to do cross-platform file monitoring:

https://github.com/guard/listen

I also made the following minor changes:
 - was calling Log.warning instead of Log.warn
 - added --udp-port for the STUN/uTP UDP socket
 - ConnectionManager.have_connection? was calling non-existent Connection.active?  I added Connection.authenticated? and used that instead.

Best,
Cotton