Merge from trunk.  Fixes #9103
Merge from trunk.  Fixes compile error in test.
Merge from trunk:
* dropped support of antique compilers
* fixed issue with ambiguity in swap (fixes #2839)
* added conditional noexcepts to move assignments, default and move constructors (fixes #7911)
* experimental variadic templates support (refs #9163)
* bunch of size optimizations for assignments and move assignments (refs #7960)
* minor changes and size optimizations
Merge from trunk: 
* dropped support of antique compilers (thanks to Stephen Kelly for doing it all around the boost!)
Merged a big bunch of internal code changes from trunk for lexical_cast:
dropped support of antique compilers, code changed to produce a smaller binaries and simplify compiler's work, simplified and shortened the code, common with other libraries code moved to 'detail/basic_pointerbuf.hpp' (fixes #9046, fixes #9070, fixes #9271)
Chrono: merge fixe for #9337.
Thread: merge missing thread move constructor noexcept.
Thread: merge missing include string.
Thread: merge dummy replacement to fix #9341.
Merged recent changes from trunk
Merged changes from trunk: warning silencing and support for SSE and C++11. Fixes #8495, #8697, #8509.
Merge r86524 (Correct broken links to C++ standard papers); fixes #9212
Merge some changes to variant that accidentaly were not merged in r86650
Merge some more changes to variant that accidentaly were not merged in r86650
Merge circular_buffer from trunk: 
* dropped support of antique compilers (thanks to Stephen Kelly for doing it all around the boost!)
avoid conflict with standard library implementations
merge trunk to release
merge trunk to release
Merge Boostbook.

- Support some colour roles (thanks to Paul Bristow).
- Support assignment return types in doxygen2boostbook. Fixes #9241.
- Fix virtual methods in doxygen2boostbook.
- Add newlines to doxygen2boostbook to make the output a tad more readable.
- Improved last-revision handling.
- Support noexcept and constexpr in doxygen2boostbook.
- Improved boostbook for virtual and explicit methods from doxygen2boostbook.
- Support `language="c++"` attribute for `code` and `programlisting` elements.
- Use that to do syntax highlighting for doxygen2boostbook.
merge trunk to release