Replace inline require shim with a file
Add testem and configuration

The test suite can now be run by installing testem globally and running
"testem" (or "testem -l phantomjs" if you have phantomjs installed to run tests
headlessly).

If you don't want to (or cannot) install testem globally, you can run
"./node_modules/bin/testem" instead.
Add section to README describing how to run tests