Add GET endpoints for users.
Factor out VersionedID from {Youdo,User}VersionID.
Factor out Versioned from Youdo and (Youdo)User.
Consistently use `thing` instead of `object`.
Move Versioned declarations to top.
Put Youdo declarations together.
Put User declarations in a better location & order.
Put TransactionID declarations with Versioned declarations.
Move DB typeclass to top.
Generalize UpdateResult.
Rename DB to YoudoDB.
Remove placeholder resource at root.
Unify get{User,Youdo} functions under new DB typeclass.
Unify posting of new items under DB typeclass.
Simplify request parsing when there's just one parameter.
Rename `withFail` to more informative `bindError`.
Add functional dependencies for DB k v m d instances.
Unify ToJSON instances for Youdo and User in responses.
Let the NamedResources be the IDs, not the Datas.
Generalize youdoURL and youdoVersionURL to resource*URL