New debugger + inital PRAM/real-time clock + fixes

- Refactored VIA rega/b implementation
  - Timers don't "work" yet, but they work a little better
  - Split rega/b into input and output versions
  - Fixed a bug that would mistake VIA1 accesses for VIA2

- Added basic support for PRAM and the RTC, although they're not
  wired into the GUI yet

- Replaced every *alloc() call with an alloc_pool call, which is
  a start toward supporting clean restarts

- Replaced ea_addr, ea_read, ea_write, and ea_read_commit with
  jump tables

- Got rid of ~inst() macro in cpu.c

- added a GLUT-based debugger