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