Improve broadening treatment

[isaacgsmith]

Many lines are not broadened accurately. Possible solutions/partial solutions:

• Include resonance broadening (this should improve the H-alpha line).
• Currently, we only use the transition's Einstein A coefficient for radiation broadening, but in theory you sum up all A coefficients of transitions that share the lower or upper level (see Rutten pg. 54). This may be too computationally expensive to implement efficiently, and it may also make a negligible impact.
• Quadratic Stark broadening should not apply to hydrogen lines. The same may apply to Van Der Waals broadening but I am not sure, we can investigate that.
• Check the existing broadening equations for accuracy.