several fixes for LHCbMath

• Fix very sad and stupid bug in the normalization of Voigt function
• provide fast approximation for Voigt fuction
• reshuffle dependency between header files to minimize coupling with GSL headers
• optmize/speedup seevral important functions
• add more coherence between C++ and python in math functions
• add several new functions [for master branch the fixes are commited via SVN]