add samples to playground

playground/TODO.md

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+
+## Todo items for the playground
+
+- [x] sample files
+- [ ] make sample files available for import
+  - workaround is to visit the file first
+- [x] move newt to a worker (shim + newt + listener)
+- [x] tabs for source, compiler output
+- [x] Show errors in editor
+- [x] show tabs on rhs
+  - [ ] editor is a tab on mobile
+- [ ] publish / host on github
+- [ ] multiple files