procedural.scm: Minor clean-up.
procedural.scm: bytestructure: Remove unnecessary arglist restriction.
procedural.scm: Don't use a parameter for
`bytestructure-descriptor-types', and add `alist-add!'.
procedural.scm: Use more normal English.

Say "ref," "index," and "set" instead of "access," "accessor," and
"mutate."
procedural.scm: Lots of changes!