Feature/milp

Implementation of an Integer Linear Program to train boolean signaling networks in order to explain experimental data.

For more details about the approach see
Mitsos A, Melas IN, Siminelakis P, Chairakaki AD, Saez-Rodriguez J, Alexopoulos LG. (2009) Identifying Drug Effects via Pathway Alterations using an Integer Linear Programming Optimization Formulation on Phosphoproteomic Data. PLoS Comput Biol 5(12): e1000591. doi:10.1371/journal.pcbi.1000591

Note: the constraint represented by equation number 2 in the paper is not implemented. Also, all the decision variables are defined as binary variables, although this condition could be relaxed for some of them as explained in the paper.