Add some very basic theory about pointed types.

This closes #220.
Move pointedType to Overture

I'm not sure if it belongs in Overture or types/Pointed, but it doesn't
belong in types/ObjectClassifier.
Merge pull request #221 from JasonGross/pointed

Add some very basic theory about pointed types.

The connection between pointedType and tomap is now clear. I am closing to allow you to continue.