Sync macos branch with master + compilation fixes

[vgmoose]

Thank you for this project! This PR is targeting the macos branch, to bring it up to date and compile/run on the latest macOS (intended to address #62).

The commit history here is overly verbose since it shows all commits from master -> macos, but it's easier to see the changes in the other direction: (from this PR -> master):

• master...vgmoose:polished-map:master

And then besides the merge commit, the new changes for the macos branch are in the last commit: 3703e39

If the merge conflicts were resolved correctly, the only main change is in the Makefile. This was compiled and tested on an M1 Pro macbook pro. I can do other tests as needed as well.

To replicate (install deps, latest fltk, build and run):

brew install pkg-config libpng libxpm
git clone https://github.com/fltk/fltk.git
cd fltk
make && make install
cd ..
git clone https://github.com/vgmoose/polished-map.git
make
./bin/polishedmap

I didn't try the Wine solution mentioned by @ss-aa-mm but it might be interesting to see how this build compares with that one in terms of functionality.