re-added lines to make sure that `bottom` and `left` are not None in
the case of `log=True`.  If this is not done, there will be type
exceptions.

Issue #1882
simplified logic related to bottom=None and log in `bar`
qt4_editor formlayout now works with colour tuples
Fixed call to path.Path.contains_point from pnpoly. contains_point accepts a list as its first argument.
Request a specific version of Gtk when using gi
Clean up text and links in screenshots page of user docs.
Tweak aesthetics of plots in screenshots page.

These changes also cleanup the code a bit, as described by MEP 12.
Add streamplot function to screenshots doc
fix pstoeps function in backend_ps.py
Added a coding_standards test module. Currently checks PEP8 compliance on all files except those explicitly excluded.
Added some of the PEP8 guidelines to ignore in the coding standards test.
Fixed failing PEP8 test.
PEP8 test only on python2. 2to3 produces non pep8 compliant code.
Fixed tests after rebase.
Merge remote-tracking branch 'tonysyu/screenshots-update' into doc-fixes-1-3

Conflicts:
	doc/users/screenshots.rst
Ensure that PY_ARRAY_UNIQUE_SYMBOL is uniquely defined for each extension.

By using a unique symbol for each extension we prevent multiple
definition linking errors which arise when statically linking
a Python interpreter.

Closes gh-2039.
Fixes a number of problems in the doc build.
Merge pull request #1889 from tacaswell/log_bar_regression

Fixed handling of `bar(.., bottom=None, log=True)`
Fixed typos in legend docs.
Tweak image path

Should fix Latex build