v0.21.0

What's Changed

• Add AudioStream abstraction to ebitengine package by @elgopher in #76
• Fix devtools glitches when pi.Update or pi.Draw are nil by @elgopher in #81
• Use Button and MouseButton types in public constants by @elgopher in #82
• Bump dependencies by @elgopher in #78

Full Changelog: v0.20.0...v0.21.0