Before routes: /JPweb-be

Method	Routes	Note
GET	/books	get all books
GET	/books/:id	get book has id = :id
GET	/books/:id/units	get all units in book has id = :id
GET	/books/:id/vocabs	get all vocabs in book has id = :id
GET	/books/:id/:unit/vocabs	get all vocabs in book has id = :id where unit = :unit
GET	/books/:id/grammars	get all grammars in book has id = :id
GET	/books/:id/:unit/grammars	get all grammars in book has id = :id where unit = :unit
GET	/users	get all users
GET	/users/:id	get user with id = :id
POST	/users	create a new user ( if failed )
PATCH	/users/:id	update user has id = :id
DELETE	/users/:id	delete user has id = :id
GET	/users/:id/books	get all books user with :id has bought
GET	/users/:id/vocabs	get all vocabs user with :id has learnt
GET	/users/:id/grammars	get all grammars user with :id has learnt