mp++ 0.27

This new mp++ release contains several new features for the real class, performance improvements for signed multiprecision integers, and a couple of build fixes.

Additionally, mp++ now has optional support for formatting via the fmt library:

https://github.com/fmtlib/fmt

The full changelog, as usual, is available here:

https://bluescarni.github.io/mppp/changelog.html