PhotoIonize API

description here.

interpolate_PI_intensity(_backRad, …)	given continuum mesh, interpolate background intensity profile
interpolate_PI_alpha(_PI_table_list, …)	given continuum mesh, interpolate photoionization cross section
bound_free_radiative_transition_coefficient(…)	Given wavelength mesh, mean intensity (as function of wavelength), photoionization cross section, compute