Fix spelling mistake
Fix minor bugs
Minor improvements to CoupledSolver
Create DirichletBC only at start of the time loop
A IPCS solver based on the cbcflow implementation.

Does not do anything useful yet.
One fix for the IPCS method. Better, not perfect
Merge branch 'next' into ipcs_solver
Merge branch 'next' into ipcs_solver
Minor documentation improvements
Merge branch 'next' into ipcs_solver

Conflicts:
	docs/opentidalfarm.solvers.rst
	opentidalfarm/solvers/coupled_sw_solver.py
Add minimal documentation to the SWProblems
Add documentation to the coupled solver
Minor edits
Copy and paste the documentation of IPCS from cbcflow. Needs updating.
Move the source terms into the Problem classes
Add the f_u to the CoupledSWSolver documentation
Adapt the IPCS documentation to the shallow water case
Align equations
Minor documentation fix
Add the relevant equation to each problem class