adds some utils functions
adds some utils functions

this adds a handful of utils functions from the 03-MRI-first-level
notebook:

 - create_sin_cpd: create a full-screen 2d sine wave, with the specified
   frequency in cpd (for a given screen radius in degrees)

 - create_circle_mask: create a circular mask of the specified size at
   the specified location

 - fit_log_norm_ci: fit log norm across bootstraps and plot the
   resulting mean and confidence intervals

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences