Added new destructuring-populate. Need to look at getters and setters for structs next
Added the concept of gl-values for complex foreign items e.g. structs.
The idea is that each foreign type will subclass gl-value for their own
type and then define their slot getter and setter methods against this.

I also tidied up some argument terminology in cffi-extra-primitive-types.lisp
Now giving a list of data to make-gl-array's :initial-contents key
then it performs a destructuring-populate. There will be no
destructuring-allocate.
Spun off glstructs into their own file
Created stubs for struct getters
Copied in the attribute-assigner generators from the old defglstruct.
This creates a function which enables and sets up the
'vertex-attrib-pointer's for the given struct type.
Added the generic gl-assign-attrib-pointers to cepl-gl-new-types.lisp
This is needed so that simple types can be used as vertex arrays.