Adds @zachallaun's test framework as submodule

[despeset]

For future testing fun! Closes #18

Are people into this?

[zachallaun]

See zachallaun/DeFacto.

[despeset]

I want to see one example of a fully working test for something we've already implemented before we pull this into master so that there is a clear path forward for testing everything.

[despeset]

But I am super into actually being able to test all this stuff – especially before we start seriously bulking up on middleware for our default stack ( see #14, #22, #15)

[zachallaun]

It seems like this could be used to very easily test middleware, which is basically data transformation. Super stateful and blocking stuff is obviously much more difficult.

I'll try to push an example tomorrow, but I may not get around to it. If anyone has the time to take a crack at it, go ahead.

[despeset]

This is now a Julia package called FactCheck – we should use the REQUIRE methodology to use the package instead of submodules.