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feature: shadow mapping, directional and spot lights #509

Job	Run time
renderling-clippy	58s
renderling-build-example	1m 35s
renderling-test-linux	3m 39s
install-cargo-gpu (ubuntu-latest)	1m 6s
renderling-test-macos	1m 29s
install-cargo-gpu (macos-latest)	1m 4s
renderling-test-windows	1m 28s
install-cargo-gpu (windows-latest)	1m 36s
renderling-build-shaders (ubuntu-latest)	21s
renderling-build-shaders (macos-latest)	23s
renderling-build-shaders (windows-latest)	30s
	14m 9s

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