Multiplayer game to collect objects on a map.

Playground is an online multiplayer game in which the player walks a map
and collects objects.

The server handles the placement of objects on the map. The client
asks the server for the objects found around a designated

When an object is returned to the client, it can be collected and is
removed from the map.

A simple REST interface to the server has been designed and documented
to encourage the development of alternative clients.