Remove obsolete scratsch directory
Get rid of d3 submodule.

There is no need to have the full d3 source in the repo. Actually, it is
only required to make the examples work, so add the dep like any of the
other deps of the examples.
Move data and lib into the examples directory.

Both dirs where there just for the examples to work, so let's keep them in
there and clean-up the top-level directory of the repo a bit.

#58