v0.2.0

This release improves performance and reliability when running large worklfows (10,000+ tasks).

What's Changed

• Add note about large workflows by @pencil in #3
• Make sure AtMostOnceBarrier only releases once (or never) by @pencil in #4
• More efficient completion callback serialization by @pencil in #5
• Always use barrier by @pencil in #2

Full Changelog: v0.1.1...v0.2.0