This is a poor man's version of the multi-instance Notifier support in
the higher level languages. It's intended primarily so that notifiers
can be created internal to the HAL.
One benefit of this change is that the current FPGA timestamp is passed
as the first parameter to the ProcessQueue function (rather than the
useless interrupt mask).
Caution for other languages wrapping the HAL: this adds a parameter to
initializeNotifier().
An atexit hook is used for safe cleanup at program termination.
Change-Id: I782b3a74c10215588ae9b7191906fb4186a81028
Implemented setTaskPriority() and getTaskPriority() in Task HAL API
Removed all other unimplemented functions in HAL and removed spawnTask()
Replaced instances of pthread_t* with TASK typedef
Removed unused HAL error constants and removed commented-out classes and functions in wpilibj's HALLibrary
Changed Task class API to match the construction semantics of a std::thread
Change-Id: I3bc951a3da90d24c5589fae4d1ca2bb60225c873
