add gitignore and remove accidentally added .swp files
Added an approximate shallow water model -- solves the shallow water model for a
single turbine in 1m/s flow and uses the velocity as a wake reduction factor.

Other minor changes to make methods more consistent.
Fix approximate shallow water model so you don't have to make a gmsh mesh for
it. Added convergence tests for wake models to the test directory. Tests are
hacky for the time being.