Stimulus smoothing

• stim_phtau - phosphor decay time constant (s) for CRT emulation,

  default value is 0.006. Currently implemented for the following stimuli:

• sine
• sine_seq
• ransinphase, ransinori, ransindir

• stim_smooth - (deg, 0.0 default - none) SD for Gaussian smoothing, beware wrap-around.
• stim_smooth_t - (s, 0.0 default - none) peak of Maxwell function (sec), beware wrap-around.