Add Travis-CI

This commit implements Travis-CI. In short, Travis-CI is a free hosted CI server that happens to integrate very nicely with Github. With this commit, any Pull Requests made will be automatically tested, saving a bit of time of having to manually clone it and test it to make sure it isn't a horrible commit. It saves some time clearing out the bad Pull Requests, and lets you focus on the ones that work. As well, it may encourage test writing for new commits, as if someone has written a passing test for their new feature, it makes it more likely to be something working and useful.

For this commit to work, you'll have to do a couple steps:

1. Go to https://travis-ci.org and sign-in using the Bukkit Github account.
2. Go to your profile (click on the name in the top right corner), and enable building for this repo.

If you have any questions, I'm happy to answer them. :boom: :smile: 

CraftBukkit PR: https://github.com/Bukkit/CraftBukkit/pull/1062