Prevents multiple types of crashes from invalid data; adds related tests

Protects against another way users could currently cause the server to crash: text messages which are not valid JSON.

This adds a few basic tests which confirm that the server can still respond to a PING from one user, after being "attacked" (sent binary messages or invalid JSON text messages) by a different user

This also adds a Travis CI configuration file, which automatically runs these tests against Node 0.11 and 0.11. You can see the relevant logs for my branch here: [![Build Status](https://travis-ci.org/jeremybanks/accidentalbot.svg)](https://travis-ci.org/jeremybanks/accidentalbot). If @cliss also enabled Travis for his master repository, this would result in the tests automatically being run against any submitted pull requests.

This doesn't include a DOS test, but I'd be surprised if a single regular user could bring down this very simple Node server with a DOS. I think the crash was more likely due to a crashing bug -- hopefully one of these two we now prevent.