[Position] Add more class methods. Add sanity check for boundaries (requires that boundaries be made known to the class).
[Entity Manager] Remove code to hide individual entities.

Only the map view is ever shown/hidden.
[Entity] Move 'Entity.position' to protect. Add a draft of 'update()'.

Also reorder initialization.
Fix some type conflicts between ints and longs.
[makefile] Add position.cpp to compilation.
[SDL Utility] Change to blended text (again?).
[SDL Entity] Utilize position getters.
[World Gen] Reduce redundant code.
[World Gen] Utilize position getters.
[World Gen] In loops, cache position coords and utilize position setter.
[World Gen] Utilize position getters. Refactor 'nextPosition()'.