Make i, j, k optional #385

Job	Run time
semver	1m 18s
Rustfmt	14s
Build Wasm Examples (wasm-yew-minimal)	49s
Build Examples (3d_charts)	32s
Clippy	2m 41s
Code Coverage	2m 16s
Build Examples (basic_charts)	24s
Tests (ubuntu-latest)	1m 57s
Build Examples (custom_controls)	38s
Tests (windows-latest)	4m 33s
Build Examples (financial_charts)	22s
Tests (macos-latest)	1m 46s
Build Examples (images)	38s
Build Examples (kaleido)	1m 10s
Build Examples (maps)	27s
Build Examples (ndarray)	24s
Build Examples (scientific_charts)	23s
Build Examples (shapes)	27s
Build Examples (subplots)	23s
	21m 22s

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