Mainly fix the estimation of the location of the extrema.

* Comment out the original minimax function at the top of the file in
  favor of the one near the bottom.
* Use lagrange to get the quadratic approximation instead of
  ratinterpol. We were expecting a simple quadratic to approximate the
  function near an extremum.
* Remove some extraneous prints, and a few more useful prints to show
  the progress of the algorithm.
* Add a few comments on how to use minimax.
* Add split_interval to insert new approximation points midway between
  the given ones.  Useful for increasing the order of an approximation
  once we've obtained an optimum.