Beam's alpha_i value can also be given as positive value now (internally it needs to be <=0 for incoming beams)

Changed convention for passing two doubles to define refractive indices: now n = 1 - delta + i beta (delta, beta are the two parameters)

Added HomogeneousMagneticMaterial class to represent magnetic materials for polarized neutron scattering

Refactored OpticalFresnel and removed inconsistency there (t should be defined such as to preserve energy); added basic stuff to enable roughness in matrix formalism

Mesocrystal test is faster now, check for BOOST version (<1.48 gives buggy PythonAPI), cmake is fully working