Changes from 2.1 to 2.2
-----------------------

 + General code tidying up and niggling bug removal.
 + Code optimisation to speed things up, although
   I haven't quantified the improvement yet.
 + Separation of the binary loader and trap handlers
   from the main program. This doesn't do anything now,
   but it will make the emulation of several PDP-11
   environments (e.g 2.11BSD, RT-11) much easier to do.
 + Finished getting the stream buffering of I/O to work.
   I still don't know why fdopen doesn't work on "rw".
 + Some extra trap functionality, e.g basic signal handling.
