Improved handling of RCON connection resets

See koraktor/steam-condenser#239
Further improve and simplify socket error handling
Fix RCONSocket broken tests
Add Gitter integration to .travis.yml
Quick fix to handle 503 from Steam Servers

The Steam servers are sometimes busy when not using the Steam API. In the case they are, it throws back a 503 and the response is not XML.

Instead of showing "XML could not be parsed", this update shows that the HTTP status is a 503 (or whatever it might be), being more helpful for the user..

Not the best solution, but it seems to be working fine for my purposes.
Merge pull request #15 from Ehesp/patch-2

Quick fix to handle 503 from Steam Servers
Add Elliot Hesp to contributors
Cleanup and improve XMLData error handling
Version bump to 1.3.8
Merge branch '1.3-stable'
Update monolog dependency to 1.10.0
Update phpunit dependency to 4.1.3