[wip] in-ns form

[thomasmulvaney]

This is an attempt to address #366

This makes in-ns just a regular function. Things seem to mostly just work, but i had to change some of the tests slightly. I think most of the issues were probably to with the deftest macro. For example the defprotocol inside a test broke unless i put a (in-ns ...) before it. Also I had to wrap some code in eval so it would end up in the foo namespace and not in the pixie.test.test-stdlib namespace.

Ideally we shouldn't have to make the changes I made to the tests. Any thoughts?

Cheers.