- Integrates Volundr's btime library and associated process scheduler
changes.
- btime is implemented separately from the process scheduler, as precise
time measurement is also useful elsewhere.
- `TimeOfHour` is no longer internally throttled; throttling is instead
done by `SCHECK`.
- If btime's `gettime` cannot be called at world startup, an error will
be output and the world will stop.
- Retains the change to schedule processes according to game time,
rather than real time.
- Removes the (now unused) update queue files.
- Removes the process scheduler testing files.
- These are standalone tests for the process scheduler, completely
unrelated to its use in the full codebase. We never used them.
- Moves the process scheduler defines into __DEFINES.
- Makes the lighting process run once before the round starts.
- Renames `scheck` to `sleepCheck`, to ensure any code that tries to use
`scheck` will fail to compile.
- Adds `SCHECK` and `SCHECK_EVERY` macros that skip calling `sleepCheck`
entirely until a specified number of `SCHECK`s (50 by default) have been
called.
- Makes most processes iterate using their `last_object` variable,
allowing hang recovery to show the type that caused the hang.
- Makes processes output an error when they filter out a type they
refuse to process.
- Rolls the recently-added alarm subsystem into the alarm process.
- Removes the now unused subsystems code.
