Add bifacial modeling capability, IV curve translation

Version 1.4: August-2018

New Functions

• pvl_Purdue_bifacial_irradiance - Calculate the irradiance on the front and rear sides of a bifacial solar module.
• pvl_Purdue_albedo_model - Calculate the collection of ground-reflected albedo light on the rear surface of a PV module.
• pvl_translate_IV_curve_IEC60891_1 - translate IV curve in irradiance and temperature using method 1 in IEC60891
• pvl_est_Rs_IEC60891_1 - estimate Rs for curve translation method 1 in IEC60891
• pvl_est_kappa_IEC60891_1 - estimate kappa for curve translation method 1 in IEC60891
• pvl_translate_IV_curve_IEC60891_2 - translate IV curve in irradiance and temperature using method 2 in IEC60891
• pvl_est_Rs_IEC60891_2 - estimate Rs for curve translation method 2 in IEC60891
• pvl_est_kappa_IEC60891_2 - estimate kappa for curve translation method 2 in IEC60891
• pvl_est_Rs_Bowden - estimate series resistance from IV curves using the method of Bowden and Rohatgi
• pvl_est_Rs_Swanson - estimate series resistance from IV curves using the method of Swanson
• pvl_est_Rs_Pysch - estimate series resistance from IV curves using Pysch's extension of the method of Swanson
• pvl_est_Rs_sunsVoc - estimate series resistance from IV curves using the suns-Voc method
• pvl_iam_martinruiz_components - Determine the incidence angle modifiers separately for beam, sky diffuse and ground reflected diffuse irradiance using the Martin and Ruiz incident angle model

API changes

• pvl_iam_physical - was pvl_physicaliam
• pvl_iam_ashrae - was pvl_ashraeiam
• pvl_iam_martinruiz - was pvl_martinruiziam

Enhancements

• pvl_perez now can return isotropic, circumsolar and horizon components of sky diffuse irradiance.

Bug fixes

• pvl_readTMY3 now correctly returns header information (thanks @shirubana).