docs: add project plan (PLAN.md) and .gitignore

.gitignore

@@ -0,0 +1,46 @@
+## Ignore Visual Studio temporary files, build results, and
+## files generated by popular Visual Studio add-ons.
+
+# User-specific files
+*.rsuser
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleases/
+x64/
+x86/
+[Aa][Rr][Mm]/
+[Aa][Rr][Mm]64/
+bld/
+[Bb]in/
+[Oo]bj/
+[Ll]og/
+[Ll]ogs/
+
+# Visual Studio cache/options
+.vs/
+.idea/
+
+# .NET
+project.lock.json
+project.fragment.lock.json
+artifacts/
+
+# NuGet
+*.nupkg
+*.snupkg
+**/[Pp]ackages/*
+!**/[Pp]ackages/build/
+
+# Rider
+*.sln.iml
+
+# OS files
+Thumbs.db
+.DS_Store