3.0.6 (stable)

Build:

• Meson build: Fix versioning on macOS
  (Tom Schoonjans) Pull request #65

Documentation:

• sigc++/sigc++.h: Describe how to use libsigc++ with Meson
  (Kjell Ahlstedt)
• Update links to the web page, now at
  libsigcplusplus.github.io/libsigcplusplus
  (Kjell Ahlstedt)