Add some tests for wrapper backend and skip some tests that are not supported by pocl.

Fix warning for `cl_khr_fp64` in OpenCL 1.2

Improved examples in documentation

Fix AttributeError: 'Win32Platform' object has no attribute 'GLX'

Rename pyopencl.ipython to pyopencl.ipython_ext to convince 2to3 that 'from IPython import' is not package-local

use the correct way to convert unicode to string. I also think this warning should be removed since it can happen when unicode_literals from __future__ is enabled.

skip scalar as shape test on pypy. [upstream bug](https://bitbucket.org/pypy/numpy/issue/10/scalar-types-should-not-be-iterable)

fix compile error for binary float function with two different input types, add tests for atan2 atan2pi

The same case is already covered by test_array.py and doesn't have to be covered here again.