tfluct as input to solver, following rp

This PR

- adds the ability to provide a _tfluct solver_ to _SharpClaw_ directly in the same fashion as Riemann solvers are passed. When `solver.tfluct_solver=True`, a fortran python-wrapped routine can be given through `import _name-of-tfluct-solver_`, `solver.tfluct=_name-of-tfluct-solver_` 
- solver follows API convention of Riemann solvers
- works in n-d
- euler_1d has been modified to provide an example of usage

This isn't a big deal, but I would actually keep the new variable names (num_ghost, num_eqn, etc.) in order to encourage developers to use them in new code.  I know that most of the Riemann solvers have not been updated with the new names.