module for opaque, extensible XS pointer backed objects using sv_magic

 XS::Object::Magic provides a way of associating structs with Perl space
 objects designed to supersede Perl's builtin "T_PTROBJ" with something that
 is designed to be:
 .
   * extensible: The association of the pointer using "sv_magicext" can be
     done on any data type, so you can associate C structs with any
     representation type. This means that you can add pointers to any object
     (hand coded, Moose or otherwise), while still having instance data in
     regular hashes.
   * opaque: The C pointer is neither visible nor modifiable from Perl space.
     This prevents accidental corruption which could lead to segfaults using
     "T_PTROBJ" (e.g. "$$ptr_obj = 0").