Switch to the BSD license

This commit switches to the BSD license all the files that
are not touched by other pending pull requests (particularly
by #6 that, if accepted, removes a number of files).

Depending on #6 destiny, another commit to switch the remainder
of the tree will or will not follow.
Make the LICENSE more community friendly

The formulation of the license with 'each severally entitled'
works best if only Arturo and I are authors, and we plan to
receive no contributions from other people.

However, IMHO such sentence -- which implements disjoint
ownership -- also discourage contributions.

On the one hand, it is not common to see such sentence into the
license of a software. If it is strange, it raises eyebrows.
If it is not smooth, it is do-something-else.

On the other hand, the community should based on a pact by which
contributors can be sure that they contributed to a commons put
under the BSD license. To implement this, shared property (rather
than disjoint property) is needed.

So, I removed the disjoint property sentence and I extended
the copyright to include all the contributors.
Merge pull request #8 from bassosimone/switch-to-BSD-license-lite

Switch to the BSD license