Move great-circle distance calculation into its own module.
Move great-circle distance calculation into its own module.

MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg,MorusAB/commonlib-fmg