the -s option can be specified to set the module to poll the SoC and
trigger a shutdown command, when a level is reached

-p and -i can be used to specify the percentage and poll interval

-c can be used to override the command (default is /sbin/halt rather
than to power off the Pi as we typically want the battery to run down
to the forced power off level so the next time power is applied, the
battery charges and power is turned back on)

-a and -b can be used to override the I2C address and SMBus number

-d can be used to print debugging information

run without options and the current state is printed

it would be nice if the program supported detaching itself and running
as a daemon but we can live without that for now