sphere_tesselate: Add another orientation; speed up incrementing

- Call st_icosahedron(pole=.true.) to get an initial icosahedron
  with the points at the poles.  This is the arrangement used
  by TERRA.
- Add st_rotate() to allow rotation of a tesselation.
- Speed up the tesselation level incrementing by reducing the
  number of points over which to search when deciding if we're
  finding a new point when having a side.
Add progs/sph_tess

This program will write to stdout the vertices or triangle sides
for an n-level tesselation, either in geographic or cartesian
coordinates.