[release] Boost 1.81.0

Release 1.81.0 of the Boost C++ Libraries is now available.

These open-source libraries work well with the C++ Standard Library,
and are usable across a broad spectrum of applications. The Boost
license encourages both commercial and non-commercial use.

This release contains one new library and numerous enhancements and bug fixes for existing libraries.
* URL: A library for parsing, modifying, and printing URLs using only C++11, from Vinnie Falco and Alan de Freitas.

For details, including download links, see
<http://www.boost.org/users/news/version_1.81.0>

You can also download directly from:
<https://boostorg.jfrog.io/artifactory/main/release/1.81.0/>

To install this release on your system, see
<http://www.boost.org/doc/libs/release/more/getting_started/index.html>

Thanks to everyone who participated in this release.

-- The Boost Release Team

Marshall Clow, Glen Fernandes, Michael Caisse