Add client interface to reqres

[thomasp85]

Currently reqres is intended for server-side use. All the niceties realted to the Request and Response classes could be nice to have as a wrapper for curl calls as well.

Some considerations:

• Should it be tacket on to current classes or be a separat (sub)class?
  • If it should be tacked on there need to be a new constructor (this might come eventually if moving broader than rook). Also the read-only nature of the Request class needs to be reconsidered. Also, the 1-to-1 link of the Request and Response classes needs to be lifted somehow.
  • If put in separate (sub)class we might miss the possibility of doing manual redirection on the server
• The obvious interface will be a send() method in Request that performs a curl call, parses the response and creates a Response object