Collision API

description here.

interpolate_CE_fac(_table, _Te, _Te_table, …)	given temperature, interpolate collisional excitation coefficient
interpolate_CI_fac(_table, _Te, _Te_table, _f2)	given temperature, interpolate collisional ionization coefficient
Cij_to_Cji(_Cij, _nj_by_ni_LTE)	calculate Cji from Cij
get_CE_rate_coe(_CE_fac, _Te, _gi, _dEij)	compute the CE rate coefficient.
get_CI_rate_coe(_CI_fac, _Te, _dEik)	compute the CI rate coefficient.