Add jspm tests and ensure support

I have no idea if it currently just works.
I guess it would be nice to have tests to prove it, like we do with other major bundlers.

As a note to keep in mind: I think that jspm states that it prefers to be pointed to the es6 src files, instead of a prebundled dist file.

No file or test path is named. Begin by locating the existing tests for other major bundlers and verify jspm’s expected ES6-source entry point; done means tests demonstrate supported jspm usage.

Written by the indexing model from the issue text.