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.

Droplet can now have different size than one and still start at zero. 
Other minor changes prior to changing units.

MAJOR BUG FIXED. x domain now starts at zero. pdepe enforces no-flux for spherical coordinates at absolute zero, not at the beginning of the domain.

Adding peaked initial conditions to ternary FRAP. Also adding figure comparing time course with steady state.

Frank's solution to probability problem via Laplace transform. Weirdly only works for one side right now.