Release v0.21.0

What's Changed

• Catch LennardJonesGenerator made NB functions. by @Lnaden in #511
• Remove logic for missing file when retrying to open a dataset by @mikemhenry in #515
• Constants codata 2018 update by @ijpulidos in #525
• deal with openmm 7.6 package unwrapping by @sroet in #528
• Overriding deepcopying behavior to avoid creating new ContextCaches. by @ijpulidos in #524
• Try closing reporter in test for windows fix by @Lnaden in #535
• Add Git Attributes File Required by Versioneer by @SimonBoothroyd in #496
• Fix for issue #435 by @mjw99 in #534
• Update changelog for #511 by @Lnaden in #512
• Testing updated python versions by @ijpulidos in #542
• ContextCache usage cleanup by @ijpulidos in #538
• Release 0.21.0 by @mikemhenry in #545

New Contributors

• @ijpulidos made their first contribution in #525
• @SimonBoothroyd made their first contribution in #496
• @mjw99 made their first contribution in #534

Full Changelog: 0.20.3...0.21.0