Results of hacking during travels: BVI, consts, word_lang

Most importantly:

 - BVI is a new intermediate language that aims to compile the globals
   state component to a dynamically extended wide ref; compiles Handle
   into Call with handler attached; integer const creation is
   shrunk. BVI is a stepping stone between BVL and BVP, i.e. the
   compilation will eventually be BVL --> BVI --> BVP.

 - bvl_const, bvp_const scripts implement certain forms of constant
   propagation (even through GC points). The optimisations are defined
   and to some extent verified.

 - A first draft of word_lang has been defined.

The files build, but many of them are still work in progress.