Change diffusion -> viscosity.
Remove quadratic_friction option - now is always True (removes linear drag support).
Rename diffusion -> viscosity in tests and examples as well.
Add a git ignore file
Ignore vim swap files
viscosity instead of viscosity_coef
Remove newton_solver param.

Since we've remove linear friction we now always have a non-linear solve which
we now always solve using Newton (removing Picard support).
Some first documentation
Remove all mentioning of Picard.
q!
Remove plot arguments from examples
Remove plot functionality
Remove some linear and picard tests
adding sub pages
Updated Documentation
Create examples.rst
Update index.rst
Merge branch 'next' of github.com:OpenTidalFarm/OpenTidalFarm into next

Conflicts:
	docs/examples.rst
Example videos
Added installation guide