Adding a test suite

I've created a QUnit test suite for this plugin. At this moment it almost only covers normal functional operation but it's a start. I think it's important to add abnormal operation tests like boundary and abuse tests.

Since autosize supports AMD I've included two test suites: index.html runs the suite with conventional script loading and index_amd.html runs the suite with dynamic loading. The test scripts themselves are the same, the one only difference is the way they're loaded.

Unfortunately I haven't run the test suite on all the targeted browsers of autosize so you're all welcome to use the test on your own browser!