Use node url module to parse db url

Resolves #71 

IMPORTANT NOTE:

I tested this with some postgres URLs locally but there might be cases where either:

1. Some task (that I don't use) in sequelize is relying on some old behavior 
2. Someone else might use a database url that is not handled by this change

So: someone who knows the internals of sequelize and the cli a lot better than I do should review this.

I didn't see any existing tests for this so I didn't write any new ones.