Log Message:
mm-common: updated to 1.0.6

mm-common 1.0.6 (2024-01-07)

* MM_AX_CXX_COMPILE_STDCXX(): Support C++20
* util/meson_aux/libstdcxx-tag.py: Try curl without compression

Meson build:
* Fix use as subproject on Windows
* Don't fail if warning_level=everything
* Meson: Donʼt fail if warning_level=everything

Skeletonmm:
* Fix the evaluation of is_git_build on Windows
* Simplify if-file-exists test

Documentation:
* Remove AUTHORS and add info to README.md