Support for more CF lineshapes

• This version allows calls to the spectrum and NXspectrum functions to specify both sigma and gamma values. If only sigma (gamma) is given, the crystal field line shape is gaussian (lorentzian). If both values are given, a pseudo-voigt line shape is used, as defined in Ida, Ando and Toraya, J. Appl. Cryst. 33, 1311 (2000).