- Fix relative imports in base of is a package or not
- Fix not working notebooks
- Add notebooks to packages sources

Used tool 2to3 to finish the porting to Python 3 plus some fixes by
hand.

These functions, which I had to implement in Python 2.2, are now
available in standard Python.

Fixed error in Chart parses method, where it would
incorrectly return some parses that did not start at the beginning
of the input (and therefore did not span the whole input).