workflow-engine v0.3.0

This release adds inter-node type casting and composite ("higher order") nodes to the engine.

What's Changed

• Add castable types by @xujustinj in #14
• Integrate typecasting with rest of workflow-engine by @xujustinj in #16
• Remove SupabaseContext by @xujustinj in #21
• Implement IfNode and IfElseNode as composite nodes by @xujustinj in #23
• Implement ForEach node by @xujustinj in #25

Full Changelog: v0.2.0...v0.3.0