Use local instead of = nil
Switch to passing the class back instead of exporting it

* The only real downsides to this are:
  * everything.moon is messier
  * it's a bit longer to import something from instead of just calling
    require
* However, the second point is a bit double edged, it also makes it more
  clear where everything is being pulled in at.
Fix a couple missing imports
Updated tutorials README
Updated example code to use the import syntax