Added get_battery to display battery status

[alvar0liveira]

Added get_battery to display battery level and status

[rachelambda]

This isn't portable, consider adding options for different OS's, such as apm on OpenBSD. Also, using a wildcard here would cause issues if multiple batteries are present.

Also, since these proc files are only one line, you might as well use read varname < filename instead of varname="$(cat filename)".