[dox] fix some MSL vs. ellpsiod alt comments
[math] geodetic_int: add extra ecef <-> enu/ned position functions

- ecef_of_enu_point_i has coordinates in cm
- ecef_of_enu_pos_i has ned in meter with INT32_POS_FRAC and ecef with cm
[state] fix local ned/enu to ecef conversion

by using new ecef_of_enu_pos_i functions which have enu in meter with INT32_POS_FRAC and ecef with cm
instead of everything in cm
[lib/ocaml] update leap_seconds

most recent leap second was inserted on June 30, 2012 at 23:59:60 UTC
So since the gps epoch 1980 we have 16 leap seconds.
[release] v5.0.2 stable version