Improving documentation: description and news files

See merge request external/cstools!37

Quantile Mapping function for CSTools

See merge request !26

Small fix to CST_RFWeights

See merge request !38

Ensclus

See merge request !33

Develop multi model ensemble combination

See merge request !27

1) function name CST_CategFc replaced with CST_CategoricalEnsCombination. 2) Additional dimension named member of size 1 added to output object to make it compatible with s2dv_cube requirements, 3) test function introduced with multiple tests, including test for dimension sizes and names, 4) documentation in CST_CategoricalEnsCombination adapted to change 2.