Log Message:
libsigc++3: updated to 3.6.0

3.6.0 (stable)

* sigc++config.h.*: Update and clean up a bit for Visual Studio
* scoped_connection: New wrapper to auto-disconnect a slot
* signal: Add connect_first()

Documentation:
* connection: Improve the class documentation
* Improve Visual Studio build documentation
* Remove AUTHORS and add general information to README.md
* manual: Add paragraph about new scoped_connection

Tests:
* Add test_scoped_connection

Build:
* Meson: Don't copy files with configure_file()
* Meson: Fix the evaluation of is_git_build on Windows
* CMake: Prevent multiple target declaration for uninstall
* Visual Studio: Support static builds
* Meson: Don't require the 'dot' command to build the documentation

3.4.0 (stable)

* Add track_object(), deprecate track_obj()
* Add trackable_signal_with_accumulator and trackable_signal

Examples, tests:
* examples/member_method: Make on_print() non-virtual
* test_accumulated.cc: clang++ requires another 'template'
* test_limit_reference.cc: Don't use auto where a slot is required

Documentation:
* signal::make_slot(): Note that signal does not derive from trackable

Build:
* Meson: Avoid configuration warnings
* Meson, MSVC: Compensate for the lack of msvc_recommended_pragmas.h
* Fix build with -Dbuild-deprecated-api=false
* Meson: Detect if we build from a git subtree
* Meson: Simplify lookup of python command
* Meson: Add build_tests option