Add possibility for max volume.

[icheered]

Using the volume-wheel on my keyboard I'm able to to set the volume way too high, to the point of extreme distortion of the sound output. It would be great if max-volume could be set in config.

[icheered]

Using something like PyBar with a volume level viewer I can see that I can literally infinitely raise my volume level. At around 80% the sound is good, around 4380% not so much...

[KenjiTakahashi]

That's interesting. It should not be possible to set volume to a higher value than the one disclosed by PA server. Does it also happen when using "standard" keyboard shortcuts (i.e. arrows and/or j/k keys)?