This commit still has active debug code!!
Bug fixes related to very hot and tenuous atmospheres (e.g., uppermost points in VAL-C), including:
   Correct definition of background source function when scattering is important
   Consistent definition of background opacities and scattering terms through all three opacity packages and both UV packages
New implementation of bezier formal solution for NLTE
Externalized optically thin and optically thick parameters for NLTE calculation
Both bezier and shortcharacteristics in NLTE now support a linear mode, activated in NICOLE.input