MAINT: use super() as described by PEP 3135

[mwtoews]

There are two common ways to use the super built-in:

1. Passing both the class and instance, e.g. super(C, self), as was required for Python 2
2. Just using super() without arguments, as described by PEP 3135, adopted in 2007 for Python 3.0

Currently there is a mixture of the two forms; find them with git grep "super([^)]" or git grep "super()". This PR refactors most of them to the PEP 3135 convention. This convention is cleaner and enforces the DRY (Don't Repeat Yourself) rule.

The two exceptions of super(cls, type) that pass a type to the second argument are in numpy/ma/core.py:

1. L3405-L3407: @dtype.setter
2. L3421-L3423: @shape.setter

These two instances cannot use a bare super(), and are not touched in this PR.

[seberg]

Thanks, LGTM, will merge it in a bit, unless someone has a comment. I never realized you can use super() for classmethods :) (or at least didn't know)