[Proj] Distance calculation

[Irwin Scollar]

Try:

Zhang Xue-Lian (1985) The nested coefficient method for accurate 
solutions of direct and inverse geodetic problems with any length. 
Proceedings of the 7th International Symposium on Geodetic 
Computations,  Direct and inverse distance 
functions.              Cracow, June 18-21, 1985. Institute of 
Geodesy and Cartography. Wasaw, Poland, ul. Jasna 2/4 pp 747-763

since it's more accurate than the classical method due to Gauss for 
long distances.

Irwin Scollar