isam - Input one sample
short isam (WVFILE *wfp, int *eof)
isam() returns the next sample from the waveform file open as wfp.
If the end of the file is reached, the returned sample value
is 0 and the flag eof is set to 1 for a "hard" eof (end of
file) or 2 for a "soft" eof (end of segment.)
H.T.Bunnell, Shirley Peters