init
get serial message flows working/closing

Allows closing when done.
closes cleanly
make every command an event emitter

Also some small cleanup of things.
Making every command an event emitter makes it simple to map flows to
their results in arbitrary ways.
simplify flows a bit
cleanup a bit
WIP: introduce chainsaw, moving things around

* move commands out to it's own module
* pay more attention to cleanup after each event
* expose fluent/chainable api to drive logic
move stick logic to it's own module

Make room for exchanging some commands.
WIP: start working on session/{Read|Transmit}Packet

Start working on basic infrastructure needed to transmit packets with this
modem.
WIP: barebones mechanics in place to transmit/read

Exchanges one message with pump (assuming power ctrl is already on).
merge
Merge branch 'master' of github.com:bewest/comlink2-uart