#16 overlap factor member in t_signal requested

[Franz Zotter]

In many situations the knowledge of the overlap factor is
desirable. Especially when working with time-constants for e.g.
spectral smoothing (tabsend-tabreceive) this is useful.

In my opinion, the two parameters s->s_n and s->s_sr in the
signal class t_signal aren't sufficient for a complete signal
processing description.
Moreover, the parameter s->s_sr isn't defined properly, as
s->s_sr=(fs*overlap) has nothing to do with the actual sampling
interval applied to the audio data.

A new member holding the signal overlap factor would be really
really great :-).