* Build script improvements.
Add NDEBUG for non-debug MacOS builds. I don't understand why, but on my system Release and RelWithDebugInfo builds were not defining NDEBUG, resulting in failing asserts and other sanity checks.
Add -jN flag to BuildLinux.sh. On my 4-core 8GB RAM system, passing -j4 allows building without a swap storm.
Improve README.md description of building on macOS.
* Merge branch 'main' into bug/macos-ndebug
* Merge branch 'main' into bug/macos-ndebug
* Merge branch 'SoftFever:main' into bug/macos-ndebug
* Improve CMake syntax. Mention Mac path to app.
* Merge branch 'main' into bug/macos-ndebug
* Improve toolpath simplification to avoid blemishes when using Arachne on thin walls.
* Avoid reducing closed perimeters below 3 points.
Downstream code contains assumptions that closed ExtrusionLines are not
degenerate. Open ExtrusionLines already are not reduced below 2 points by
ExtrusionLine::simplify().
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Co-authored-by: SoftFever <softfeverever@gmail.com>