make plot in Sampling_example.ipynb be site means

[Swanson-Hysell]

The example shown in Sampling_example.ipynb generates samples from 10 sites with 4 samples per site

params0 = smp.Params(N=10,
                     n0=4,
                     kappa_within_site=100,
                     site_lat=10, 
                     site_long=0,
                     outlier_rate=0.10,
                     secular_method="G",
                     kappa_secular=None)

All of these samples are then plotted which makes them look like independent samples. It is uncommon to plot sample data while skipping the site hierarchy as done here. I think that it makes sense to either generate the sample with n0=1 or to calculate a site mean for each site. This would need to be done in directional space and then transformed to VGP space.

It also seems valuable to have this example show the angular error from the true pole for the sample. This would be illustrative.