Test dependencies

[MarvinNazari]

Wonder if we could add Quick and Nimble as test dependencies, would make the whole process faster! we can use Carthage for that.

[JohnSundell]

Great suggestion @MarvinNazari! We shouldn't assume that every project will use Quick, Nimble & Carthage, but we could add options for specifying what dependencies you want to use, and which package manager. 👍

[KieranHarper]

I've had a crack at this in PR #58