Large commit: model fits, basic grid methods

Code for full model fitting with f2py and to explore parameter space of
B0, eta2, mu. Add interactive manual fitting, sketch out grids for fits
Add and test code to compute 1-D "mesh" on arbitrary function; will
be used to grid over B0 at fixed eta2, mu.
Fix grid code for negative step in f'n range
Add code to grid full model parameter space

Apply previous gridding code to full model function (f2py'd) and
checked for reasonable output with simple and full model codes.