Making pyDAL independent from web2py and a pip package

Some notes:

* I've put myself as the pip package maintainer (setup.py), if someone else on the team would like to do that, feel free to propose yourself
* AUTHORS should be filled in
* We need to port tests from web2py
* integration under web2py need to rewrite some imports, and to check contrib modules that uses/implements stuffs under `DRIVERS`
* Maybe we want to add a dedicated documentation?

@mdipierro Should be easier to merge this before everything else and then redo PRs from latest web2py's DAL