initial work on implementing packet radio interface.
can open and read from TTY.
doesn't do anything with the data yet.
doesn't write proper packets to the interface yet.
doesn't use bitrate config option yet.
refactored packet radio code mostly into separate file.
began writing stateful packet decoder.
setup serial port mode when opening packet radio interface.
(now reads bytes over serial line)
add hook for transmitting packet via packet radio interface.
make serial port non-blocking (which for some reason has also
killed our ability to read from it :/).
fixed serial port reading and interface setup bugs.
now crashes when trying to tick packet radio interface.
fixed problems with interface ticking on packetradio interfaces.
still crashes and burns.
added safety catch for null message field.
note that debug.packettx seems to be broken.
more work on SLIP encoding/decoding for packet radio interfaces.
closer to working.
POLLOUT seems to get stuck once triggered.
fixed handling of POLL flags on packet radio interface
(was not calling watch() when changing them).
fixed some packet radio encapsulation bugs.
prune some debugging.
avoid some segfaults due to lack of IP addresses in packet radio
native MDP payloads.
problems remain with SLIP encapsulation/extraction, but some packets
are already getting through.
hex constants are easier to read than octal.
debug encapsulation.
decoder state bug fix.
Throttle serial radio devices when tx buffer is in use
Never send a unicast probe over a packet radio link
Calculate neighbour score based on tick interval

Quick hack for packet radio links which should have a much longer lived relationship between neighbours
Don't aggregate packets together on radio links
Only advertise BAR's on an alarm

- we no longer hit the database for every outgoing packet, attempting to announce bundles
- we no longer advertise manifests periodically
- when an interesting bar arrives, we ask for the manifest to be announced, which uses the existing packet format
added simple fake radio driver with ~100ms latency.