Use of wait_for_current_time_update to sequence feds with acyclic interfaces

[trevorhardy]

For federates that do not have cycles in their interfaces (e.g. a sequence of controllers where the output of one feeds the input of the next), you can use wait_for_current_time_update on all but the first in the sequence to achieve a defined order of operation (time grants). They would all be granted the same simulation time but will receive those grants after all their dependent federates have completed execution at that timestep. That is, the dependency graph between the federates effectively defines the order of time grants.

We need an example on this.