Adding new classes - AnalyticSolution, NeumannBoundaryCondition, DirichletBoundaryCondition, LinearDiffusion, RightHandSide, TimeFunction, ZeroRightHandSide
Updating classes (implementation of partial derivations) - SinWaveFunction, ExpBumpFunction, SinBumpsFunction
Updating classes (modifying and adding new methods) - SimpleProblemSetter, SimpleProblemSolver
Modifying - simple-solver.cfg.desc

Changing explicit solvers - Merson and Euler.

There is gap of missing commits.

Adding edge-skip to grid comparison function.