allow keyword access to array instances.  arrayfields works by adding
only a few methods to arrays, namely #fields= and fields, but the
#fields= method is hooked to extend an array on a per object basis.  in
otherwords __only__ those arrays whose fields are set will have
auto-magical keyword access bestowed on them - all other arrays remain
unaffected.  arrays with keyword access require much less memory when
compared to hashes/objects and yet still provide fast lookup and
preserve data order.
