The script facdemo.g illustrates the use of the facsynchan object, and may be
run by typing "genesis facdemo".  Like the hebbsynchan, the facsynchan is a
variation of the synaptically-activated channel object, synchan.  As
explained in greater detail in the facsynchan documentation, it can exhibit
synaptic facilitation, synaptic depression, or some combination of the two.

In this demonstration, a simple spike generator sends a steady stream of
spikes to a "facsynchan" object.

The facsynchan object can exibit both facilitation and depression at the same
time, with different values of the facilitation per spike (fac_per_spike),
depression pre spike (depr_per_spike), and different time constants for the
decay of facilitation (fac_tau) and depression (depr_tau).  However, in this
demo, the choices are either facilitation, depression, or neither.
