Add to parser the possibility to define arbitrary convex functions

[saramagliacane]

Use simil-Breeze syntax, for example:

math.pow(math.max(coeffs.dot([votes(anna, demo), votes(bob, demo), friends(anna, bob)]) - constant, 0),2) *weight

Allow arbitrary functions, the user is responsible to check that they are convex.

[saramagliacane]

possibly allow also the grounding: math.pow(math.max(coeffs.dot([votes(A, P), votes(B, P), friends(A, B)]) - constant, 0),2) *weight