Goals for 1.2:

* Create tess2vtk to export a tesseroid file to VTK and vtk2tess to go back
* Better documentation on Using Tesseroids. Describe each program, its input and
  output, and what its used for.
* Add sanity check of -s argument on tessmodgen
* Add checks for NaN values in the input functions

TODO:

* Add the custom ratio recipe to the cookbook
* Add docs for the -t option
* Add program tesssplit to break the tesseroids in a file into smaller
  tesseroids. Useful when using tess2prism to convert tesseroids that are too
  large (the computation points would endup inside the resulting prisms).
* Clean up Doxygen markup from the comments and code
* Check error in not rotating prism
* Check error os using tesseroid in poles
* Programs to calculate the effect of a sphere model in spherical coordinates
* Program to calculate geoid height from potential using different ellipsoids
* Make minunit into functions and put variable arguments for messages like printf
* Test adapt using a whole Earth against a sphere
* tessgrd: Catch wrong order of -r arguments ie. w > e or s > n
* prism_grav: Unroll loops in gx and gy

Ideas:

* Make a program tessgrdspc that gets the grid spacing and checks if it is regular
* Make a version of tess_grav that doesn't use the glq module. Instead, it uses
  a fixed order 2 and the tabulated values of the nodes and weights. Bonus,
  it subdivides the tesseroids automatically using a pile (lifo).


BUGS:
