`random_shuffle` randomly rearranges the elements in `rng`. The versions of `random_shuffle` that do not specify a `Generator` use an internal random number generator. The versions of `random_shuffle` that do specify a `Generator` use this instead. Returns the shuffles range.
[heading Definition]
Defined in the header file `boost/range/algorithm/random_shuffle.hpp`
[heading Requirements]
[*For the version without a Generator:]
* `RandomAccessRange` is a model of the __random_access_range__ Concept.
[*For the version with a Generator:]
* `RandomAccessRange` is a model of the __random_access_range__ Concept.
* `Generator` is a model of the `RandomNumberGeneratorConcept`.
* `RandomAccessRange`'s distance type is convertible to `Generator`'s argument type.
[heading Precondition:]
* `distance(rng)` is less than `gen`'s maximum value.
[heading Complexity]
Linear. If `!empty(rng)`, exactly `distance(rng) - 1` swaps are performed.