Update version number

isort change

Update changelog

Fix ronaldoussoren#334: Also include arm64 stubs in distribution arch…

…ives

Set version

Issue ronaldoussoren#281: App won't launch on macOS 10.9 or 10.10

Version 0.21

Don't advertise support for old python versions

Fix test failures

Remove explicit support for botocore, but autodetect vendored version…

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