- Add PPC512/640 emulation
- Add TV display type to Sinclair PC200
- Add font selection to PC1512
- Add disc change line to PC200
Patch from JohnElliott
The new code is based on timestamps, rather than delays. This eliminates the
need to update every timer in timer_process(), which cost a non-trivial amount
of CPU time on low-end machines.
This involved changes to every user of the timer code, so this change almost
certainly introduces bugs.
