Mermaid.NET.Flowcharts 4.0.0

What's Changed

• 60-update-readme by @JansthcirlU in #62
• 63 add non generic subgraphcreate factory method to be backwards compatible by @JansthcirlU in #64
• 61-fix-duplicate-node-adds-in-graph-and-subgraph-add-link by @JansthcirlU in #65
• 66-prep-release-400-due-to-breaking-changes by @JansthcirlU in #67

Full Changelog: 3.1.0...4.0.0