Refactor to use composer.json, namespace, support php 5.3 and remove features.

Hi, I don't know if you have interest in our changes, but I guess you may want to take a look, we did a lot of things on this big refactor:

- Added namespace with your initials DX
- Added composer.json to repo (we use http://getcomposer.org/ to manage our dependencies)
- Renamed a lot of variables trying to give a better meaning to them
- Removed features: no union, no intersect, no merge, no info, no element count.
- Applied our code standards, spaces, brackets, documentation blocks.
- Removed the interface.
- Removed static methods.
- Updated constructor to do the same thing createFromProbability was doing.

Maybe I forgot something, but they are on the diff.

Thanks for your working library!

Cheers,