Add todo and example todo

exampletodo.txt

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+- (A) Call Mom @Phone +Family
+- (A) Schedule annual checkup +Health
+- (B) Outline chapter 5 +Novel @Computer
+- (C) Add cover sheets @Office +TPSReports
+- (D) correct priority is highlighted
+- (d) incorrect priority is not highlighted
+- A simple key:value field
+- Most of these example tasks were adapted from url:http://todotxt.org/todo.txt
+- Plan backyard herb garden @Home
+- Research self-publishing services +Novel @Computer
+- d2018-09-20 Pick up milk @GroceryStore
+x Download Todo.txt mobile app @Phone
+x2018-09-18 c2018-09-17 A task with completion date and creation date

todo.txt

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+- c2018-09-18 Sort tasks by completion, priority, due date, description
+- c2018-09-18 Quit using Esc or q
+- c2018-09-18 Offer "retry" or "quit" +dialogue - syntax error in todo file
+- c2018-09-18 Offer "retry" or "quit" +dialogue - couldn't load from todo file
+- c2018-09-18 Offer "retry" or "quit" +dialogue - couldn't save to todo file
+- c2018-09-18 Offer to clean up file when loading (adding creation/completion dates)
+- c2018-09-18 Purge - move completed tasks to a separate file