[C++] Access Economy params

[lamer]

AI's interface provides access to economy parameters with Economy::GetCurrent, ::GetIncome, ::GetUsage and ::GetStorage.
Lua's interface has access to more params like Pull, Share, Sent, Recieved, Excess. If no one objects i'll add those params to C interface (although i have no idea what's Pull and Share).
At the moment i want to use only Recieved, but i can't see any reason to hide others from AI.

Edit: Done