Merge pull request #40 from Manishearth/test

Forward test to master: adding Event class
Specifies [dev] dependencies as an "extra" in setup.py, per #42.

Updates Makefile so that dev dependencies are not installed when running
the example, but are installed when running the tests.

This leaves us without any automatic testing ensuring that the standard
dependencies are correct, but under manual testing (of the example) this
setup is working as intended.
Merge branch 'dev-dependencies' into test