Feature/Optimize combination helpers

[jsconan]

Rewrite the combination helpers in a more efficient way.

They now expect values starting at 0. This will allow using the helpers with indices instead of final values.
The combinations are sorted in lexicographic order but right-to-left instead of left-to-right. This simplifies the signature as the number of possible values is no longer required.

Algorithms have been borrowed and optimized from:

• https://math.stackexchange.com/questions/1363239/fast-way-to-get-a-position-of-combination-without-repetitions
• https://math.stackexchange.com/questions/1368526/fast-way-to-get-a-combination-given-its-position-in-reverse-lexicographic-or