Don't specify d3 as a git submodule.

We'll soon add a package.json file which properly defines deps.
Add a license (file)
Add a package.json file.
Make ugglify a dev depdenceny.
Slight improvements to the Makefile.

* Make sure that all generated files are removed on clean.
* Use the npm installed ugglify
* Make sure that both the extended and the minified versions are generated
  on make all.
Add an .gitignore file and ignore node_modules directory.
Add some wrapper code which defines the public API.

* There is now also a default configuration for the algorithm. Which is for
  now the only one.
Update d3.treemap.js and add the minified version as well.