fixed relative links in docs

fixed relative links in docs

Merge pull request #293 from boostorg/fix/upgrade_droneubuntu2404

updated cppalliance/droneubuntu2304 to 2404

Merge pull request #293 from boostorg/fix/upgrade_droneubuntu2404

updated cppalliance/droneubuntu2304 to 2404

[skip ci] updated benchmark plots

[skip ci] updated benchmark plots

Merge pull request #238 from boostorg/fix/gh-237

Fixed bug in the `const` version of `unordered_multimap::find(k, hash, eq)`

Fixed support for allocators with `explicit` copy constructors (#234)

* added tests for explicit allocators

* made explicit_alloc_ctor_tests work
by adhering to the principle that classes templated with Allocator should accept exactly Allocator objects

* removed TMP machinery older compilers choke about

* initialized variables

* updated release notes

* fixed PR number

[skip ci] editorial

updated boost::unordered_[multi]set and boost::unordered_(flat|node)_…

…map benchmarks