Timing considerations in ThetaStim

    outer loop:

outer_event
outer_on
outer_ispike

public variables:

outer_interval
outer_number
outer_start
outer_noise

    inner loop:

event
on
ispike

public variables:

interval
number
start
noise

General timing flow (assuming that the outer_number and number are >0):

First outer_start is used to initiate an outer_event
The outer_event initiates an event at “start” time later (start time now refers
to a delay from each outer_event
The events play out as in an ordinary netstim.  When done the next
outer_event is initiated.