Files match namespaces

Cleanup namespace naming as follows:

* All namespaces should be hyphenated
* All filenames should be underscorized
* Add namespaces to example files where they were missing
* All namespaces in example files should match the namespace used in the tests
* All requires and imports should happen in the ns macro

Also included:
* Cleanup whitespace
* Remove a few extraneous requires
* prefer `:require` over `:use` in ns macros

This is a fairly big set of changes, however, they mostly occur in namespace macros and are intended to make the problem set more consistent. While going through the Clojure exercises, I became frustrated with the inconsistency of the names and namespacing of required files. This seeks to rectify that.