Merge pull request #23 from cider-team-mercury/latex_materials

Added elastic profiles, with shear modulus used to generate them (from MaO et al. 2001)
Changed SPlines to produce more "Physical" looking energy.
Added Melt Fractionation and Checked all equations in
mantle_evolution_with_fixed_crust.py for bugs, found one relating to the
the volume of the convecting mantle rather than the volume of the
stagnant lid.
switching back to gleason and mao, and trying more iterations to fix energy derivatives.
fixed merge conglics on mercury_interior_structure_model.py