Also switches to using a parametrized test, for better error messages

* Review F401,F841,F842 flake8 errors (unused variables, imports)

* Review comments

* More tests in test_installed_npymath_ini

* Review comments

This adds entry_points for the f2py scripts. The installed scripts
differ between Windows and other environments.

* On Windows, the only script installed is 'f2py'. This works well in
  that environment because each Python version is installed in its own
  directory, making it easy to keep the differing script versions
  separate.

* Otherwise, three scripts are installed, 'f2py', 'f2py' + 'minor', and
  'f2py' + 'major.minor'. For instance, if Numpy is installed by
  Python 2.7, then the installed scripts will be named 'f2py', 'f2py2',
  and 'f2py2.7'. That naming scheme is used for back compatibility, and
  also so that more than one Python version can be dealt with in a way
  common to many Linux distros. Note that 'f2py' will always point to
  the latest install and 'f2py(2|3)' to the latest Python (2|3) install

The script tests have been modified to check for the new environment
and the code previously used to install the scripts has been removed.

Use standard pytest markers everywhere in the numpy tests. At this point
there should be no nose dependency. However, nose is required to test
the legacy decorators if so desired.

At this point, numpy test cannot be run in the way with runtests, rather
installed numpy can be tested with `pytest --pyargs numpy` as long as
that is not run from the repo. Run it from the tools directory or some
such.

The aim here is to separate out the nose dependent files prior to adding
pytest support. This could be done by adding new files to the general
numpy/testing directory, but I felt that it was to have the relevant
files separated out as it makes it easier to completely remove nose
dependencies when needed.

Many places were accessing submodules in numpy/testing directly, and in
some cases incorrectly. That presented a backwards compatibility
problem. The solution adapted here is to have "dummy" files whose
contents will depend on whether of not pytest is active. That way the
module looks the same as before from the outside.

In the case of numpy itself, direct accesses have been fixed. Having
proper `__all__` lists in the submodules helped in that.

Bare except is very rarely the right thing