add support for negative index in child paths
add support for negative index in child paths

if child index is negative it indicates an offset from the end of the
children array, i.e. -1 means 'last child'

pirxpilot/liftie,code42day/liftie,pirxpilot/liftie,code42day/liftie,pirxpilot/liftie,code42day/liftie