Update to Readme re Statistics + Raggiana; also bumps finagle versions

Added some notes to the readme gleaned from the user group

* https://groups.google.com/d/msg/iago-users/CNQx1i3vjNQ/mMpyK8BORfwJ
* https://groups.google.com/d/msg/iago-users/tkDk7RMqzAk/DeKCNBBlQVYJ
* https://groups.google.com/d/msg/iago-users/wlcKhMQfUlU/_3cVwHsS6J0J

Also bumped the versions of finagle in the pom. For me, one extra test failed, but I didn't have the time/expertise to investigate.

Bumped in the hope that Iago would exit if the server-under-test gave any timeouts (https://github.com/twitter/iago/issues/21) - didn't work, but I forgot to revert this... but perhaps the dependencies should be bumped?