Move REF-FORM to common code.

Exposed octet-vector types; added constructors

* package.lisp: added exported symbols octet, index, octet-vector,
  simple-octet-vector, make-octet-vector
* types.lisp: added type octet; added functions make-octet-vector and
  octet-vector
* tests.lisp: use make-octet-vector instead of make-array where
  possible

This change is necessary for making nibbles work well with ironclad.

These tests currently take too long; next step is to make them reasonable.

We used a dword register to manipulate the value, but then we attempted
to move said register into a qword register, which the assembler rightly
complained about.  Rename the incoming value register, so we can have
its qword and dword names available simultaneously throughout the body
of the VOP.

If the user wants to use lists, they should be able to do that.

I'm happy about the functionality; I'm not satisfied with the names,
because I also want to add destructive versions of these ala
READ-SEQUENCE.  But we can tinker with that later.