About half way done with implementing [[pairing]]. The webapp's interface
to prompt for a secret and start pairing is done; the protocol is
implemented; broadcasting of pairing requests is working; added Yet Another
Thread to listen for incoming pairing traffic.

Very happy with how this came together; starting with defining the protocol
with data types let me rapidly iterate until I had designed a simple, clean,
robust protocol. The implementation works well too; it's even possible to
start pairing, and only then bring up the network interface to the machine
you intended to pair with, and it'll detect the new interface and start
sending requests to it.

Next, I need to make alerts have a button that performs a stored
IO action. So that the incoming pair request alert can have a button to
respond to the pair request. And then I need to write the code to actually
perform the pairing, including ssh key setup.
