Initial commit: UserStringProperty Rhino plugin

- Rhino 8 C# plugin for managing Block UserString properties
- XML template import with merge modes
- WinForms UI for property editing
- .NET Framework 4.8

.gitignore

@@ -0,0 +1,25 @@
+# Build results
+
+bin/
+obj/
+
+# Visual Studio
+.vs/
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Rider
+.idea/
+
+# VS Code
+.code/
+
+# Rhino plugin output (should be .rhp, not tracked)
+*.rhp
+*.dll
+
+# OS
+Thumbs.db
+.DS_Store