GitLab

It is especially useful for themes, this function is a port of the code written by Steve Losh
and made available on [this blog entry](http://stevelosh.com/blog/2010/02/my-extravagant-zsh-prompt/#my-right-prompt-battery-capacity)

Define empty functions instead of none at all if we can't figure out the
platform.

Separate the battery_pct_remaining data into it's own function so that it can be obtained even if the battery is connected.

linux battery level now refreshes after every command