Allow rate limiting raw CAN messages.

This is a a breaking change to a few different APIs, and it also adds a
test for the example passthrough implementation in the repo.
Add forceSendChanged flag to CanMessage and use in passthrough handler.
Use the minimum allowable type size to save memory.

Incremental progress in #162.
Merge branch 'next' into force-send-change-message-overflow

Conflicts:
	src/can/canutil.cpp
Merge branch 'next' into force-send-change-message-overflow

Conflicts:
	src/can/canutil.h