* Drop Py2-only Array.__nonzero__

* Adapt docs to absence of Array.__nonzero__

* cl.array.ravel: take order as an argument

* adds test ravel

* Enable flake8-bugbear

* Remove two more attempts to iterate/cast options

https://github.com/inducer/modepy/pull/38#issuecomment-846472970

Extend cl.array.(maximum|minimum|if_positive) to take scalars

- always return 'out' even when the user provides a buffer for it

- probably cleaner to read
- probably better performance (?)

np.number is a Number