Cleanup

[pca006132]

A list of cleanup to do before v3.0.

• [ ] https://github.com/elalish/manifold/blob/master/RELEASE_CHECKLIST.md
• [x] Cleanup .vscode/launch.json.
• [x] Move the public header install logic to the main cmake file?
• [x] Remove the single mesh file in extras/Thingi10K/raw_meshes.
• [ ] Organize extras, e.g. move things related to hull testing to its own folder, add readme to explain the use of each file.
• [x] format.sh format cmake.
• [x] Remove .gitmodules.
• [x] Update readme about the clang-format version requirement.
• [x] Workaround #944 by adding ignore flags.
• [ ] Try to make fuzzing work again.
• [ ] Check the documentation to make sure things are up-to-date.