In vNext, it'll be time to remove the tr1 namespace, which we've deprecated for a long time. This mostly consists of using-declarations. However, <random> contains actual machinery, like the old uniform_int which powers the modern uniform_int_distribution. We need to remove the old stuff while overhauling this header.

vNext note: Resolving this issue will require breaking binary compatibility. We won't be able to accept pull requests for this issue until the vNext branch is available. See #169 for more information.