9c75ee6b3b
Fix formatting specifiers doc links d36e3e23a80f039ee98117ebba0bb2ea6e34f0c1 seems to have inadvertently changed many of these links to point to `core::fmt` instead of `std::fmt`. The information about formatting specifiers is only documented in [`std::fmt`](https://doc.rust-lang.org/std/fmt/); [`core::fmt`](https://doc.rust-lang.org/core/fmt/) is empty. 3baf6a4a749bd6ac4a8b9f1054d3f2ad2fc91e45 seems to have already fixed a couple of these links to point back to `std::fmt`.