Define a fork with N
alternative subtrajectories.
branch(.trj, option, continue, ...)
Arguments
.trj 
the trajectory object. 
option 
a callable object (a function) which must return an integer between
0 and N . A return value equal to 0 skips the branch and
continues to the next activity. A returning value between 1 to N
makes the arrival to follow the corresponding subtrajectory. 
continue 
a vector of N booleans that indicate whether the arrival must
continue to the main trajectory after each subtrajectory or not. 
... 
N trajectory objects describing each subtrajectory.

Value
Returns the trajectory object.