Enable battery on Mac OS X

This uses ioreg to read the battery status.  This was tested on
Mac OS 10.8.3, but will probably work a few versions back as well.
Update mac-battery support to use pmset instead of ioreg

pmset's output is much closer to the point.
Merge branch 'develop' of github.com:nojhan/liquidprompt into develop

* 'develop' of github.com:nojhan/liquidprompt:
  Update mac-battery support to use pmset instead of ioreg
  Enable battery on Mac OS X

Conflicts:
	liquidprompt