(mu, lambda)-CMA-ES optimizer implementation 

Here's a (mu, lambda)-CMA-ES optimizer implementation. I had to modifiy the arg creator class in order to convert between numpy arrays and the MetaOpt specific domain model (with args). It is working for me. 
The mutation strength is global and is fixed to 0.5. We have to discuss how to handle meta parameters like mutation strength (in the meeting). Please review and add comments.