Randomize example driver

When there are multiple actions with the best score, pick one randomly.
This makes the game more interesting.
Prefer going forward over turning

Give higher score if driver can go forward and pick a penguin later over
switching lanes and picking penguin later, which may lead to colisions
with other cars.
Handle exceptions in driver code

Previously if a driver function raised an exception, the client was
reconnecting and a twisted traceback was printed. The twisted traceback
included too much irelevant information that can make it harder to
understad the error in the driver function.

Now when driver is raising an exception, we print more clear excpetion,
and keep the connection to the server.
Use config.port instead of hardcoded value.
Decouple game from server

I would like additional ways to control and query the game, such as web
interface and xmlrpc interface. To implement this, the game should be
created outside the server.
Add XMLRPC interface for controling game server

Previously to start a game you had to start all the clients, then start
the server. The server would start the game when the first client
connected. To stop the server you had to stop the server process. This
caused players to get another car for each game and sometimes a player
could start one iteration after other players, depending on the timing
of starting the players.

Now you start and stop games using the new XMLRPC interface. A new
rtp-admin tool supports start and stop commands, and can be used
remotely.

Now players get a certain car when they join the game, and continue to
use the same car for all games until they disconnect.

As part of the xmlrpc interface, we have a web server. Currently it does
not serve any content, but it can be used to display the game
scoreboard.
Update readme

Explain how to start and stop races using the new rtp-admin tool.
Merge pull request #61 from nirs/examples

Improve example drivers
Merge pull request #62 from nirs/driver-errors

Handle exceptions in driver code
Merge pull request #63 from nirs/web

Add XMLRPC interface for controling game server