Calling HALSIM_PauseTiming pauses the FPGA clock and notifiers.
Calling HALSIM_ResumeTiming resumes the FPGA clock and notifiers.
Calling HALSIM_StepTiming steps the FPGA clock and runs applicable notifiers.
This will effectively pause TimedRobot and any other notifier-based events,
but of course will not pause user threads that do not use the notifier (e.g.
image processing).
This allows high-level library classes to implement enhanced simulation
support even if no low-level corresponding simulation library exists, and
avoids the need for bit-banging complex interfaces like SPI or CAN.
The 2019 FPGA image switched the output of auto SPI from plain bytes to a
sequence of 32-bit words (timestamp, then words with the byte values in the
least significant byte of each word).
In addition to changing the HAL and simulators to reflect this, add piecewise
integration support to wpilibc/wpilibj SPI to take advantage of the timestamps
and use it in the ADXRS450 gyro.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
