Moved the sequence start and stop logic into the button_end function.
This will allow the sequence to stop without firing a final frame after
the sequence is done. Also added variables to define the speed of the
motors a little more easily.
as opposed to when it is first pressed. It is with great consternation
that I make this change. The original intention of the Trigger()
feature was to be instant, but having used the intervalometer on
several rolls now, I find the extra frame that this feature introduces
into sequences to be troublesome.