Some plotting updates.

o mu_2 is now reported as sqrt(mu_2) because this is the same as standard
deviation.
o All plots now share same x-axis

Also added support for fitting z_d
Updated scale length variable names to match Xilouris.

Also updated default values of scale parameters to match Xilouris' V band
data (had been using I band before for some reason).
A lot of updates to Coltrane. Plotting and analysis.

Main changse:
o Plots now have better axis limits, etc.
o New function mult_zd creates a grid of starting parameters to cutting
seesion. This takes a long time
o Cutting session now returns the final chi squared value
New module for getting moments from SALT data that are model independent

It only has one function for now, but it's a pretty sweet function!