WIP: Establish "canon" of exemplary Kwant scripts

We may decide to break backwards compatibility, but doing so should be a well-informed choice. Unfortunately, it has arrived to us to break backwards compatibility involuntarily.

In order to avoid such situation, I propose to establish a body of scripts that that have been disseminated as examples of good Kwant usage and represent a wide spectrum of Kwant usage.

Note that the script canon is complementary to unit tests: the latter focus on correctness (even of corner cases) and are typically updated to the most modern API usage. The canon, on the other hand, is static and concentrates on typical and exemplary usage.

What do you think of the overall idea?

So far the canon contains scripts from the 2013 NJP paper and from the March meeting tutorial. It could use some scripts that show off Kwant features like KPM, discrete symmetries and magnetic field. @anton-akhmerov, what do you think about adding code from the topology MOOC? Any other exemplary codes that come to your mind?