New derivation of equations, including weak form statement. mshr and spherical mesh only work on python 3.6 for now. Changing initial conditions, time step, grid size can all influence stability of algorithm.

Adding new file with Cahn Hilliard extended to Flory Huggins binary mixture. This was used in email to Chris.

Amended Cahn Hilliard code in a minimal way to account for Flory Huggins binary mixture with the corresponding mobility scaling. Seems to work, but not sure about the volume fraction to concentration conversion.