Adding some convenience functions to Span and Endpoint classes.
one more convenience function for Endpoint that returns java.net.InetSocketAddress (host/port combo)
added return types for new functions
Added unit tests for my new functions and consequently discovered a bug in how I was converting
signed to unsigned.  Fixed the bug and consequently decided to not convert integer values in
binary annotations because I don't really know where they come from, and the caller might want them
still to be signed.
Merge pull request #235 from twitter/zipkin-common-enhancements

Adding some convenience functions to Span and Endpoint classes.