Added the "BSD-2-Clause" license

The "2-Clause" variant of the BSD license is an OSI approved license:
http://opensource.org/licenses/BSD-2-Clause
changed the "BSD<X>" labels into "BSD-<X>-clause"

Changed the "BSD<X>" labels into "BSD-<X>-clause" equivalent according
to the recommandations of the DEP5 specifications:

http://dep.debian.net/deps/dep5/#license-specification
Merge pull request #32 from blue-prawn/master

Added the "BSD-2-Clause" license, change BSD3 and BSD4 to BSD-3-Clause and BSD-4-Clause.