Merge branch 'api-design'

See !16
4 jobs for v0.2.0 in 2 minutes (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #44057
test package

00:01:47

passed #44059
test package with latest SymPy and Kwant stable

00:02:00

passed #44058
test package with latest scipy

00:01:54

passed #44060
test packaging

00:01:44