updated the internal API for how grids are constructed to simplify the code

add option such that when resolution==0, the resolution is calculated automatically from the sample list.

add delete_grid_variable function

In my CEMP simulations, I use the above with something like this to zoom in around 0.8Msun in M1:

emp_population.update_grid_variable(
    name="lnm1",
    spacingfunc="gaussian_zoom(np.log(0.4),np.log(6.0),np.log(0.8),0.05,0.99,100)",
    resolution=0
)

Processed alot of what pylint suggested. Might change the naming conventions rules tho, the short parameter names are an issue, but lets not get too strict..

added some plots, restructured routine for scalingplots, fixing the phasevol part of the grid generator

played around with arg list. copied defaults from perl into defaults.py to include the physics defaults in the arg_string