Print the optimal friction of a single turbine.
Add a new callback option "config.statewriter_callback", with which the user
can define a callback function which will be called at every timestep in the
forward shallow water equation with the pressure and velocity solution
as arguments. This can be used for performing diagnostics, saving the solutions
in custom file formats or other purposes.
Merge branch 'master' of https://github.com/funsim/OpenTidalFarm into wake_models
dirty commit -- midway through fix and want to be able to work at home