Merge pull request #70 from kalmarek/mk/characters_ring_str #462

Job	Run time
Julia 1.6 - ubuntu-latest - x64	6m 50s
Julia 1.6 - macOS-latest - x64	10m 51s
Julia 1.6 - windows-latest - x64	14m 58s
Julia 1 - ubuntu-latest - x64	6m 59s
Julia 1 - macOS-latest - x64	7m 45s
Julia 1 - windows-latest - x64	8m 8s
Julia nightly - ubuntu-latest - x64	8m 46s
Julia nightly - macOS-latest - x64	14m 26s
Julia nightly - windows-latest - x64	9m 29s
	1h 28m 12s

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