[API] Add the `resource` route helper

[rsamoilov]

Description

The resource helper allows to add a singular resource to your routing. With it, the resource :profile call would generate the following routes:

Method	URL	Action
GET	/profile/new	new
GET	/profile	show
PATCH/PUT	/profile	update
DELETE	/profile	destroy
POST	/profile	create

Tips

• The change should be done in lib/rage/router/dsl.rb.
• Check the architecture doc that shows how Rage's core components interact with each other.
• Feel free to ask any questions or request help in the comments below!