Bots can now move around

[Andrey Levushkin]

Hi, I've just pushed some engine code into the repository that enables the bots to turn and accelerate and the arena updates their position. There are also a bunch of other methods that are stubbed out and need to be filled in so if any one wants to have a go at filling them in take a look in Engine.hs. 

In the process of adding the above I've imported the AC-Vector library as previously discussed so now most bot properties are vectors. 

In addition to that I've also pulled in the fclabels Lens library as it made the  stepBotState function much cleaner. Now most of the records defined in Core.hs have lenses associated with them. Have a look at http://hackage.haskell.org/packages/archive/fclabels/1.1.4.3/doc/html/Data-Label.html to learn more about fclabels. You can still use records with lenses as ordinary records.

Andrey