setdiff_all: Get the difference of two vectors in both directions.
Description
The base-R function `setdiff` is asymmetric meaning
`setdiff(vec1, vec2)` is not the same as `setdiff(vec2, vec1)`.
Only the first vector will be compared to the second vector and all
elements not contained in the second are in the resulting vector.
So if you also want in include all elements being in the second vector
but not in the first, you can use this function. In this case you are
searching for elements being in the union of both vectors but not
in the intersect of both vectors. This function is a symmetric function.
It doesn't matter in which order you input the vectors, the content
will be the same. Only the order of the elements inside the output
differs.