Doc: + dg_mosaic, stereo_mpi, dem_geoid, point2las, more on DG
Minor wording cleanup of dg_mosaic and stereo_mpi
Minor doc cleanup
Spell
Doc: More geoid/areoid and cleanup
stereo_tri: dgmaprpc: Have caching happen correctly

I goofed and my prior idea of pre-caching the point cloud wasn't
working becuase I didn't use the correct type.