Hide aggregation to parent type

[steinybot]

You may also want to discuss this in Ideas.

Description

When a type A extends another type B and also defines a member of type B there is both a generalisation and association relationship. It would be nice to hide the association.

This would allow the diagram to be simpler and hide unnecessary arrows.

Potential Solution

This should be a new rendering option.

Additional Information

This won't be very useable until #14 has been implemented.