ALSA volume widget

This widget uses amixer to get and set the current volume level and it also exports functions you can use
in keybindings to change the volume and mute / unmute your soundcard.

To add this widget to your configuration, insert
    require("obvious.volume_alsa")
into the top of your rc.lua and add obvious.volume_alsa() to your wibox.

Optionally you can specify the cardid and channel to be controlled like this:
  obvious.volume_alsa(cardid, channel)

the default channel is "Master", you might need to set it to "PCM"

Safe the object returned from obvious.volume_alsa() and call
    obj:raise()
    obj:lower()
    obj:mute()
on it with keybindings.

If you want to use the data gathered by this widget, you can use the function
obvous.volume_alsa.get_data(cardid, channel).
It returns nil on failure, otherwise it returns a table with the following fields:

    volume  a number representing the current volume from 0 to 100
    mute    a boolean value describing whether the channel is muted or not
