Bug 15980 – std.traits.Identity is undocumented but public

The `Identity` alias defined in std.traits is publicly available (I discovered it through a selective import in a downstream project), but not documented in any way: https://github.com/dlang/phobos/blob/1e9fdc08f5dac1e7cd87919bd408164dd2084370/std/traits.d#L3260 I'd happily fix the problem directly with a PR, but I'm not sure quite what the purpose of this symbol is, so reporting it here as a first step.

Commits pushed to master at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/3a322792bfc7488b05c0ddd9515e83e9bd04b009 Fix Issue 15980: std.traits.Identity is undocumented but public https://github.com/dlang/phobos/commit/edd157a3b41a872ea5c047fbdee61fdf37c1b91a Merge pull request #4279 from JackStouffer/issue15980 Fix Issue 15980: std.traits.Identity is undocumented but public