All existing plugins are added to the binary bundle, in their latest
version, so that users don't need to pip install tutor.
Also, the tutor MANIFEST.in file was removed to simplify the management
of package data.
Close #242.
Replace all make commands by a single "tutor" binary. Environment and
data are all moved to ~/.tutor/local/share/tutor. We take the
opportunity to add a web UI and revamp the documentation.
This is a complete rewrite.
Close #121.
Close #147.
