start using a common base class
use the CFFI:USE-FOREIGN-LIBRARY form
Package cleanup;

 * export only legitimately interesting public symbols (maybe add more
   later, but this is a starting-point)

 * hide C wrapper functions in a separate package

 * wrap CFFI:DEFCFUN so we can do a few things, like pushing the symbols
   into BULLET-PHYSICS-C++ package and making sure they're UNINTERN'ed in
   BULLET-PHYSICS
adjust to new format
fix license (for this package itself) and re-order BT-LOAD-LIBS
clarify license
tutorial / unit test