edit: Let the writer handle \n in text; drop unprintable runes
edit: Implement point (cursor as seen by user)
edit: Remove Editor.refresh
edit: Comments
eval: Keep the point as index into string
edit: Point-aware editor operations
edit: point -> dot, in spirit of acme (or maybe sam...)
edit: Implement Left and Right
edit: Support Ctrl-K
edit: Comment, cleanup
edit: Make prompt, line, tip and dot part of Editor