added some functions to compute KL distance + documentation
updated the KL and calibration functions
first version of tau.lowup.KL
new functions to minimze KL + new graphs
first version of KL_divergence_chisqstrech
new generic functions

these function allow to ajust n.of.y and tau.lowup of specified
equivalence test by minimizing the KL between power and summary lkl.
Doc and examples are provided.