Don't start up w/ the first four channels on...  We only want that
for the LED to let us know it's running...

Turns out that the base TimeoutError is different than the asyncio
version, and so we weren't actually retrying packets, just terminating
early...

both take a shared key as an argument...

the respondent arg (-r) takes an argument specifying the function to
call w/ the messages...  The form is: module_path[:name.of.func].  If
the name is not specified, func will be used.

This just makes sure things are a little tighter wrt protocol
compliance, ensuring that a corrupted initiator doesn't do bad
things..

This also adds a check to make sure that the allocated structure matches
the C code so that things won't break.

This breaks out the session state into it's own object... allowing a
common function to handle the state machine...

This also adds a new powerful testing tool.  It's a Synchronization
primitive that will ensure blocks of code run in the expected order,
and only run when the previous block has fully run...  This helps
ensure ordering between many tasks, to cause race conditions that
would otherwise be hard to cause..

are ignored, and it triggers a resent of the previous packet...

Turns out there's a bit of code that isn't compatible w/ the Python version,
eliminate it...  This was to support encoding lengths (via negative length
parameters)...

Also, the default C version (which we want to use) is Keccak(800) and not
Keccak(1600), switch Python to 800, as it'll be faster on the 32-bit uC, and
still has plenty of security margin...