Make libffi-type-pointer a slot and method, define for built-in types

1. Idea: Make a slot for libffi-type-pointer and define for all
built-in types, then define methods to make the pointer on demand for
other type classes.
2. Add slot [libffi-type-pointer] with generic function to defclass
foreign-type. 
3. New file [built-in-types.lisp] defines all built-in types, and
libffi-type-pointer :around method for typedefs/aliases.
4. New [libffi-type-pointer :around method] for foreign-struct-type.
5. New lists exported from CFFI for possible other uses, and needed
here: *other-builtin-types* *built-in-integer-types*
*built-in-float-types*.