Redirect from the previous crab project to the new one

[pl h]

It would be very helpful to put a pointer from old crab to current one:

https://github.com/muricoca/crab

New users are more likely to find the above one first.

The pointer on this INSTALL page ( http://muricoca.github.io/crab/install.html ) is also misleading: pip install -U crab

The current "crab" on pypi is something else: https://pypi.python.org/pypi/crab