vector sorting tests and docs

In the process of trying to nail down the docs for the Vector sorting constants, I ran into some inconsistencies and posted about them in the [forums](http://loomsdk.com/forums/troubleshooting-and-issues/topics/bug-tracing-result-of-vector-sort-uniquesort-gives-segfault). This PR provides unit tests to drive the expected behavior for `Vector.sort()`.

Also included are the docs updates, some cleanup around gem installing / ignoring, and the addition of assertion error messages to the console and junit xml when running unit tests.