delete the Hexabus-USB code
remove useless README
split contiki code and hexabus platform apps and code
fix contiki config and datetime service

contiki-config: set to 125 ticks per contiki second, while
126.008something happen. that's why our clock was so phenomenally wrong
all the time.

datetime service: add the concept of leap seconds and use that correct
the error that bumping CLOCK_CONF_SECOND didn't fix.
remove datetime service getTimestamp()

duplicates functionality of clock_seconds()
clean up Socket platform makefile
change HEXABUS_SOCKET platform number, remove _USB
oops, don't skip a month
remove remnants of the rf212 driver
Merge branch 'pb-contiki-update' into development