Add REST API endpoints related with collections

[rgaiacs]

Requires:

• Document collection endpoints in https://stoplight.io #148
• Add controller related with collection #86

Create file src/rotas/collection.js, following good practices, and add:

POST

• /api/v1/collections

GET

• /api/v1/collections
• /api/v1/collections/{slang}

PUT

• /api/v1/collections/{slang}

DELETE

• /api/v1/collections/{slang}

Remember to write tests, see #94, and document the endpoints in docs/rest_api/collection.rst.