2.99.12: (unstable)

* Avoid compiler warnings from function pointer conversions
  (Kjell Ahlstedt) Issue #1 (sharkcz)
  (Kjell Ahlstedt) Issue #8 (db0451)

Build:
* Replace the Visual Studio project files with MSVC NMake project files
  Add MSVC_NMake/README.txt for Visual Studio builds
  (Chun-wei Fan) Pull request #7
* cmake: Require C++17 support
  (Kjell Ahlstedt) Issue #9 (telkamp)

Documentation:
* Update links in README, configure.ac, libsigcplusplus.doap
  (Seirra) Pull request #4
  (Kjell Ahlstedt)
* README: Update compiler requirement
  (Kjell Ahlstedt) Issue #6 (Petr Ohlidal)