Fix namespaces

[benfb]

It’s frowned upon to use use in production code, but it’s handy when you’re experimenting in the REPL and you want to quickly get your hands on some functions
– http://www.braveclojure.com/organization/#Requiring_and_Using_Namespaces

This would be a fairly large undertaking.

Right now, external namespaces are used in push rather than required. This causes side effects.

Actually changing uses to requires would be relatively easy, but old code would also need to be migrated somehow, so I'm not sure if this is actually worth it.

Still, isolating namespaces would be friendlier and more idiomatic.

Thoughts?

[lspector]

I've been a slow convert to require, and while I still prefer use in many contexts with small projects, I agree that Clojush has grown too big for this. But changing this would indeed require a fair bit of work.