spergel profiles are much slower than galsim

[beckermr]

I've heard reports that the spergel profiles are much slower than galsim.

To Do:

• add benchmark comparison to galsim
• profile to find optimizations
• implement those optimizations

[ismael-mendoza]

quick note, when I checked it was a sum of Exponential and Spergel profile (nu=-0.6) -- might be worth taking a look at the timing of each of these separately, but my guess is that it's very likely coming from the Spergel...