#2282: gallery examples use low-order integration n Multipole

Comment (by Erik Schnetter):

The DriscollHealy2D rule is the best rule we implemented. It has spectral accuracy.

The so-called midpoint rule doesn’t implement the midpoint rule and is only 1st order accurate, different from the documentation.

Most integration methods neglect the fact that the domain is periodic in the phi direction and introduce unnecessary errors there.