mixer volume setting

[ibotty]

> I have adjusted the script to create mixer.conf if the directory is
> writeable. The mixerctl script is gone. Thanks, this is useful :)

i did not create that file by default, to have a mean to disable that
script.
if we do so, we might need a MIXER_VOL_ADJUST=<bool> or something like that,
to en-/disable this.

(not a big deal, but for the sake of completeness ;)

~ibotty

PS: sorry for this clumsy mail...