Merge pull request #6 from Goffredo/master

Add margins to widget.
Beautiful integration

Default color values can be overridden by theme values:

theme.apw_fg_color
theme.apw_bg_color
theme.apw_mute_fg_color
theme.apw_mute_bg_color
Mixer support

Mixer command ("pavucontrol" by default) is executed when
widget is right-clicked.

Mixer command can be customized by calling :SetMixer() on the widget.
Update documentation for mixer and theme support

Updated README.md to reflect new mixer and theme features.
Mixer fixes

Changed mixer command to "LaunchMixer()"
Corrected spaces/tabs issues.
Documentation fixes

Removed hanging semicolon in code snippet.
Added note about the need to run beautiful.init before requiring apw.
Setting default margin back to 0.
Add comment on customizing APW.
Widget now changes color (and doesn't respond to volume manipulations)
if pulseaudio is not running.