Clean up examples

[florisvb]

The examples directory looks quite daunting. We should clean it up so there are maybe 3 good notebooks in there, which are all referenced in the tutorials and maybe some kind of gallery, too.

A separate directory could include a more extensive list of notebooks to illustrate more advanced features.

[psilentp]

I've created an examples section in the documentation, currently the image links are broken on github (they work ok when the documentation is generated locally). Maybe they could be autogenerated ala matplotlibs examples.