Make i, j, k optional #386

Job	Run time
Clippy	3m 5s
Code Coverage	1m 58s
Build Examples (3d_charts)	24s
Build Wasm Examples (wasm-yew-minimal)	55s
Build Examples (basic_charts)	28s
Rustfmt	11s
semver	3m 44s
Build Examples (custom_controls)	58s
Tests (ubuntu-latest)	2m 30s
Build Examples (financial_charts)	25s
Tests (windows-latest)	4m 47s
Build Examples (images)	45s
Tests (macos-latest)	1m 50s
Build Examples (kaleido)	1m 12s
Build Examples (maps)	21s
Build Examples (ndarray)	23s
Build Examples (scientific_charts)	36s
Build Examples (shapes)	29s
Build Examples (subplots)	24s
	25m 25s

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