Scala dist maven

[This is mostly done, but won't have time until Wed to finish it.
Already letting the bot have a look, and (p)reviewer @gkossakowski.]

The idea is that a Scala distribution is a simple repackaging of artifacts already available on maven.

We already publish the following to maven: typical jars for the artifacts (classes, sources, scaladoc).
This PR adds: the bin/, doc/, and man/ directories, packaged up in scala-dist.

To simplify this, move the contents that should end up in the distribution
from docs/ to doc/, create the man/ directory with the manpages,
and include the scripts in bin/.

These directories are packaged in the scala-dist jar and published to maven,
with a dependency on scala-library-all and scala-compiler,
for the jars that should end up in the distribution.

This way, a scala dist can be built by resolving scala-dist,
and moving all the class-file jars of its depencies to lib/
(use api/ for scaladoc jars, and src/ for the source jars).