Add the capability to create tagged pointer and classes in bitmanip

Create utilities to make safe tagged pointer and class references in std.bitmanip.
I didn't catch this before, but you seem to omit that this other generator is for tagged classes instead of pointers.

Stupid question -- is there a reason we have to have 2 different names? They seem so very similar, only dependent on the fact that one is a class and one is a pointer.