In the future, we want to allow users to rely on third-party services
for data storage, such as hosted MySQL and such. To do so, we need to be
able to configure the host/port of these services, which we do here.
This is to address part of #114.
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.
