added LBFGS solver for L2

@fuentesdt 

I have added an L2 solver that uses the LBFGS.
It needs a function evaluation and the gradient. The gradient can be computed using FD.
I have added an example to the test_TV_min. It seems to work but is super slow.
Right now it also can not solve constraint problems. 

P.S. I tried matlabs fminunc, but it runs out of memory on my machine.