Add unsafe_getindex and unsafe_setindex! #335

Job	Run time
Documentation	1m 15s
Julia 1.6 - ubuntu-latest - x64 - push	1m 12s
Julia 1.6 - macOS-latest - x64 - push	2m 52s
Julia 1.6 - windows-latest - x64 - push	10m 44s
Julia 1 - ubuntu-latest - x64 - push	58s
Julia 1 - macOS-latest - x64 - push	2m 27s
Julia 1 - windows-latest - x64 - push	1m 35s
Julia nightly - ubuntu-latest - x64 - push	1m 51s
Julia nightly - macOS-latest - x64 - push	3m 6s
Julia nightly - windows-latest - x64 - push	6h 0m 1s
	6h 26m 1s

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