Set the natural width of the column from the child's one to what is needed for the child to reach the maximum allocatable width.
This not only makes more sense but it will allow HdyColumn to serve as a container setting a natural size to its child by giving the same value to the maximum width and the linear growth width.
This also fixes the minimum size request of the column by ensuring it doesn't allocate less width than its child requires.
Fixes #87 (closed)