Use EXT_SUFFIX instead of SO for py_limited_api renaming

Use LegacyVersion instead of LooseVersion

- Also apply the patch for numpy 1.11.2 pre release

Use LooseVersion instread of StrictVersion

Remove private prefix from monkey as monkey module explicitly declares that all functions are private.

Use pytest>=3.0.2

The bug that lead to pin it (pytest-dev/pytest#1888) was fixed in 3.0.2

Install py.test>=2.8,<3

The 3.x series is currently broken. Until py.test works again, 3.x
should not be used by anything.

Make Extension accept positional arguments again (fixes #752).