Log Message:
libsigc++3: update to 3.0.3.

3.0.3 (stable)

Build:
* docs/docs/reference/meson.build: Check if perl is found
  (Kjell Ahlstedt) Issue #53 (Rasmus Thomsen)
* README.md: Describe building with Meson
  (Kjell Ahlstedt)

Examples:
* Add example of using libsigc++ with Qt
  (Robert Middleton) Pull request #35

Tests:
* Replace C-style casts with static_cast<>
  (Lennard Berger)

3.0.2 (stable)

* Build: Meson build improvements.
  (Kjell Ahlstedt, Chun-Wei Fan)

3.0.1 (stable)

* Build:
  - Add meson build, alongside the existing autotools and CMake builds.
  (Kjell Ahlstedt, Chun-Wei Fan)
  - CMake: Fix the MSVC build, enable warnings, and disable unnecessary
  warnings, with MVSC.
  (Stuart Dootson)
* connection: Allow copying of empty connections.
  (Aigrind)
* sigc++/adaptors/bind.h: Make bind_functor::bound_ public.
  (Used by sigc::visitor::do_visit_each().
  (Kjell Ahlstedt) Bug #26
* test_limit_reference: Avoid virtual-move-assign warning
  (seen with g++ 9.2)
  (Murray Cumming)
* signal: slot_iterator_buf: Remove unused T_result default type
  (Murray Cumming)
* tests: Slight cleanups
  (Murray Cumming)
* Remove unused #ifdefed code.
  (Murray Cumming)