Improve the overall build system, including Makefile and CI

[grunt-lucas]

• Add support for Windows via MSVC? MinGW?
  • Apparently it is possible to build a cross-compiled version with minGW on a macbook:

    brew install mingw-w64
    cd porytiles
    make clean && CC="x86_64-w64-mingw32-gcc" CXX="x86_64-w64-mingw32-g++" make

  • you can extract this and steal the libpng.a file https://packages.msys2.org/package/mingw-w64-x86_64-libpng
• set up package caches so installs don't have to run every time
  • probably too hard to do with homebrew, apt
• Mac universal binary?
  • https://stackoverflow.com/questions/67945226/how-to-build-an-intel-binary-on-an-m1-mac-from-the-command-line-with-the-standar
• better build system? (cmake? autotools? etc)
  • https://cmake.org/cmake/help/latest/guide/tutorial/index.html
  • https://stackoverflow.com/questions/68105648/configure-cmake-to-work-with-homebrew-libraries-instead-system-provided-librarie
  • https://cliutils.gitlab.io/modern-cmake/
  • https://github.com/ttroy50/cmake-examples/tree/master
• static analysis: https://nrk.neocities.org/articles/c-static-analyzers