Issue Description:

There's currently an inconsistency between the raw and typed unsafe pointer APIs on what kinds of pointers can be used to deallocate memory. Of the typed pointers, only UnsafeMutablePointer has a deallocate() method, while both raw pointers, UnsafeRawPointer and UnsafeMutableRawPointer, have deallocate(). Adding deallocate() to UnsafePointer is an additive change.

In addition, both raw buffers have deallocate() methods that deallocate all the referenced memory, but neither typed buffer has such a method (although if the typed buffers can deallocate they probably also need to be able to deinitialize...).