* Extract Permutation functions from the Statistical class into a dedicated Permutations class
Retain the original methods in the Statistical class as stubs for BC, but deprecate them. They will be removed for PHPSpreadsheet v2
Note that unit tests still point to the Statistical class stubs; these should be modified to use the Permutations class directly when the stubs are removed
Also provided a basic implementationof the PERMUTATIONA() Function
Mark Baker
Adrien Crivelli