Change router scheme to always echo

Some logic is hard to prove right. This patch changes router.c to 'be stupider' instead. Any time a data interrupt is taken, we do all possible things that could be related. For PC_INT0, we echo the rPi outward and the current dispenser back toward the rPi.

Note, even if the current dispenser is tied to INT1, when INT0 fires we still read the current state of our target dispenser line, and set the outbound to the same level. This will cause extra work (due to extraneous interrupts), but is shorter and easier to argue correct.
Remove state checking from rPi communication as well

Forgot to remove the state checking from the rPi echo code as well. Remove it and other dead code, move rPi echo into its own function.
Merge pull request #77 from raylee/master

Re implement ISR handling in the router to be simpler and faster.