fix typo in figlegend_demo.py

otherwise y4 never gets used
include PySide in qt4agg backend check
MNT : slight refactoring of Gcf

Use classmethods instead of staticmethods to implement the
singleton in `_pylab_helpers.Gcf`.
fix E251

Signed-off-by: Thomas Hisch <t.hisch@gmail.com>
Remove use of PyCXX in core C++ extensions
Change how array converter functions are defined
Add .clang-format to repository
Restore parallel testing
Documentation
Remove some obsolete TODOs
Fix compilation
Remove debugging prints
Fix curve simplification
Fix segfault on Python 3
More Python 3 fixes
Windows-related fixes, thanks to @cgohlke
Fix test_hexbin_pickable test
Fix Mac compile again
Remove usage of old Numpy API
class foo: => class foo(object):