fade
Apply fade in and fade out to a signal

Usage:

y = fade(signal,rise_time,fs);
[y, window] = fade(signal,rise_time,fs);

`signal`	Input signal. Size: (time x channels).
`rise_time`	Fading time (in s), applied each to beginning and the end of the signal.
`fs`	Sampling frequency (in Hz).

`y`	Output signal. Size: (time x channels).
`window`	Column vector with the window used to create the fading.

fade(..) imposes a cosine-like fade-in and fade-out to the begining and end of a signal, respectively.