Estimate the Strehl ratio for a PSF.
This requires computing a simulated PSF with the same properties as the one under analysis.
Note that this calculation will not be very accurate unless both PSFs are well sampled, preferably several times better than Nyquist. See Roberts et al. 2004 SPIE 5490 for a discussion of the various possible pitfalls when calculating Strehl ratios.
HDUlist_or_filename, ext : string, int
center : tuple
print_, display : bool
cache_perfect : bool
strehl : float