Clean up Dependencies

[arb]

Finalize dev vs run dependencies. Lock down versions where appropriate.

[AdrieanKhisbe]

@arb, Do you want me to take care of this in #34? :)

[arb]

Nah, this can be it's own thing. Really we want to be clear on dev vs actual dependencies. Since this module has a build step, it's not immediately obvious which dependencies you need where.