'sim' is a small simulator for the bootloader's update code. It tests
untimely powerdowns to ensure that the bootloader will recover from a
power loss or reset at any time during the boot.
Note that, as of this commit, there are some failures in the test that
need to be investigated.
Also note that this build script does not output proper dependencies for
source files outside of the simulator directory, and won't rebuild the C
files if they or headers are modified.
David Brown