target types need to be formalized

[RyanHedges]

Currently target types are constants on a class but we are now asking questions and keying off actions based on target types. We should formalize this into some class with initializers and methods like:

explicit? none? set? not_set? value

[drewdeponte]

I started down this path and halted to work on other things which are more important. If someone wants to pick up where I left off I have a branch called, formalize_target_types which has the beginnings of a formalized TargetType with some methods.

I am sure it needs to evolve quite a bit further. But, it is at least a start.

[drewdeponte]

BTW, it implements all of the above methods.

[drewdeponte]

Lets punt on this for v3.0.0 so we can have more time to think about how we would ideally like to do this.