exp10 is a GNU function, is not part of C++, and is not available
everywhere.
pow(10,x) is an alternative that works just as well. It is used in musl as
the implementation of exp10.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
ensure that valid mixer values are set also when the ALSA driver
does not report a valid dB range ('set_raw' fallback)
correct a bug in which volume is assumed to lie in [0..100]
instead of [0..1]
Due to rounding errors, a slightly negative value can be passed to
set_normalized_volume(), which will make the log10() call fail.
Actually, volume 0 is already failing because log10(0) is illegal. So
let's fix this by implementing two corner cases: <=0 and >=100.
Closes#212
