Deps update and small fixes

Fix deprecation warning for String.slice/2

API has been stable for a while, marking it as 1.0

Add type aliases for latitude and longitude

documentation improvements

neighbors/1 now returns a map instead of a keywords list

within/2 now expets two tuples for coordinates

Fix coordinates ordering, always use {lon, lat}

Add Geohax.within/2 to calculate geohashes within an envelope

Add neighbors-finding functions