Create a Shrt by PUTing with json body

Shrts are now created by PUTing to the /shrts resource:

  curl -XPUT
       -H "Content-Type: application/json"
       -d '{"uri":"www.gmail.com"}' 'https://localhost:9000/shrts'

Also, a bug has been fixed whereby the protocol part was messed up when
explicitly provided.