 o fix new() bug pointed out by "Paul" at inline@perl.org
 o allow assignment to _HASH & _ARRAY (but not _KEYS)
 o change names of _HASH, _ARRAY, and _KEYS (to what?)
 o add a _TIEHASH accessor?
 o allow nesting of structures which aren't _pointers_
 o #define support?
 o type checking in accessors
