Please document hana::transform side effect ordering

GCC appears to evaluate transform function calls out of order, which I think it's allowed to do because function argument evaluation order is undefined. Hana should explicitly document the lack of ordering guarantees in transform.

Locate the documentation for hana::transform and review its existing description of invocation behavior. Document that transform provides no ordering guarantee for its function calls, then verify that the wording accurately reflects the reported GCC behavior.

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