Added the LMLS cost function and generalized the cost function

I generalized the cost function: I believe it's better for everyone, who can customize the behaviour of the mlp

I added LMLS: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=478411&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D478411
Write what the abbreviations stand for (i.e., mean squared error, mean absolute error).
Btw, the paper calls it "mean log squared error (MLSE)", where does "LMLS" come from? MLSE seems more consistent with the other errors.