Issue 300 robin neumann bcs

[valentinsulzer]

Fixes #300

[valentinsulzer]

By the way, is there a way to have "Plots" installed without it being added to the Project.toml?

[ChrisRackauckas]

You could add it as a test dependency, but plotting shouldn't be in the tests at all?

[valentinsulzer]

When I want to plot something to check it, I need to add Plots, but then it gets added to Project.toml so I have to remove it if I want to do git add .. I guess I could just git add individual folders and files

[ChrisRackauckas]

I always just ]dev it and you never have that issue.

[ChrisRackauckas]

Looks great. I think we'll want to split the docs apart to multiple example files and such soon, but that's a separate issue and not a reason to hold this up.