fixed timer triggering error with clauses like 'TIMER > xx'
take more to care to check multiple subconditions for the minimum timer value to set
  a trigger for.
minor change to the calculation used to sleep cw in its main loop. cw cycles at more or less a 1k sample per sec.. more changes in this area later
add a return value for the LEAVE token
add a LEAVE state action clause.
this feature is disabled if DISABLE_LEAVE_FUNCTIONS is defined, in which case LEAVE actions raise errors
as long as DISABLE_LEAVE_FUNCTIONS is not defined, io components now raise on_leave and off_leave events to support the ‘LEAVE state action’ behaviour
generate state_leave messages and send them to dependent machines just before changing state or updating the TIMER value.
add an example of the LEAVE clause