Ignore unused files
move processing script to scripts directory
Add covariance functions
Calculate covariance parameters - first working version

Note: the gradient has a local discontinuity at r=0.
Would it be better to not provide the gradient?

Note 2: I also tried trust-region-reflective.  It was very slow (200+
steps, and hadn't got anywhere near the expected solution when I gave
up).
Covariance param optimization - refinement

This is faster and better without the gradient!

Also, fix lower bounds - all hyperparams should be >= 0.
Merge branch 'master' of github.com:sdewet/gaussian_regression_project