API Summary

operation	HTTP method	Request Body	Parameters	Recursive
show todos	GET	-	completed, parent	-
create todo	POST	{value, parent}	-	-
mark todo as completed	PUT	{id}	-	on all children
delete todo	DELETE	{id}	-	on all children

• Since the API is utilizing HTTP method, there is only one URI: /api/todos
• All request and response bodies are formatted as JSON.

TODO

• atomic save for recursive update/delete
• better input validation

• middleware of mongoose of .pre('save'...)