Removed hashCode() override from Datum class - it does not override equals(), and should not override hashCode(). The isEqual() method could be renamed or rewritten to override equals, but is currently does not.
Added hashCode() override to Unit class and Pair class.
Added override annotations to Ellipsoid class for clarity.
Signed-off-by: neutlamberink gijs.vd.neut-lamberink@rigd-loxia.nl