location API only provides horizontal API but iOS/OSX API supports
both horizontal and vertical. Maybe consider implementing vertical
accuracy for Android by hand later
and get_longitude are gone now in place of get_position. Basically,
from C land we basically do a poll-style queries, but on the
implementation side (ie. Android/iOS/OSX) - they all use callback-based
location updates. So we simply check in the poll function (get_position)
whether position has changed, and if so, update the pointer values and
return true - if not, set them to 0 and return false.
