add ways-to-add-up-to to "math" module

[amtoine]

at my job, i studied very quickly something that involved computing all the ways one can build a positive integer from the addition of other positive integers.

enters the ways-to-add-up-to command i've written and added to the math module in this PR.

example

ways-to-add-up-to 4 will be [[1, 1, 1, 1], [1, 1, 2], [1, 3], [2, 2], [4]]] because $4$
can be obtained as follows:

$$ 1 + 1 + 1 + 1 $$

$$ 1 + 1 + 2 = 1 + 2 + 1 = 2 + 1 + 1 $$

$$ 1 + 3 = 3 + 1 $$

$$ 2 + 2 $$

$$ 4 $$

Note
$1 + 1 + 2$ and $1 + 2 + 1$ are considered the same because addition is commutative and thus only [1, 1, 2] will be returned

[fdncred]

Thanks