v5.1.1

What's Changed

• Test {fmt} using header only so it actually runs in CI by @mborland in #983
• Fix sign processing bug in {fmt} by @mborland in #987
• Fix to_chars rounding for 0.999... -> 1(.0000) by @mborland in #989
• Fix sign parsing with <format> by @mborland in #990
• Fix formatting support so that we can format into the middle of a string by @mborland in #992

Full Changelog: v5.1.0...v5.1.1