Convert photometry module docstrings to NumPy style

Convert all :param/:returns: style docstrings to NumPy style
(Parameters/Returns/Raises/Notes sections) across photometry.py,
photometry_measure.py, photometry_model.py, photometry_psf.py, and
photometry_iraf.py. Also adds estimate_fwhm robust FWHM estimator
and converts its docstrings.

Author: karpov-sv