Implement IEC61853 IAM calculations

[adriesse]

The standard gives the option of using interpolation of measured data, or the Martin & Ruiz model which has the single parameter a_r. Both should be implemented.

[cwhanse]

The Martin and Ruiz model is in PVLib for MATLAB. In a later paper Martin and Ruiz extended the model to estimate reflection of diffuse irradiance, also in PVLib for MATLAB here I think both versions are useful, the component version shows up in various bifacial irradiance models.

[cwhanse]

#679 and #680 are relevant