Add unit tests (and DOM tests for #808)

One of the problems that I've found with Raphael is that there isn't a unit test suite. Over the years I've found many regression bugs that could have been easily prevented. Also, without having a very intimate knowledge of Raphael, it's hard to contribute without knowing if something else broke :fearful:.

This pull requests adds the `dev/test` folder structure. Depending on the browser, tests from `dev/test/svg` or `dev/test/vml` are loaded. We could also add a `dev/test/core` folder for shared tests that would be loaded in both browsers.

I use Raphael as one of the core libraries on one of my projects. My knowledge of Raphael's innards is growing so I'd like to contribute more tests since this was just a quick subset to get the PR created :smile:.