This makes callback registration completely thread safe.
This patch also uses templates and macros to dramatically reduce the amount of
manual boilerplate.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
Added callback scheme for a pass through to something higher
level. Since the ID is embedded into the arbitration ID, and some
devices can use different schemes whether it is plugged in through a
device or put into the daisy chain (pigeonImu), I made one "internal
data object" for max reusability.
