Add class method to create Rectangle from a given object

This will help when detecting collisions with AABB.
Begin using a Collider class that will detect all collision detections
Core::BulletDispenser should dispense out of sight bullets
Use more idiomatic ruby names
Remove map size constant since it could be determined in other ways
Use the Core constants whenever possible

Writing the same numbers in those constants may not make it obvious
that they are the same as those in Core. Therefore writing out the
Core constants path will make it evident.
There is no need to granulate the module in require files
Require statements need a little rearrangement