Set matplotlib backend globally
Create matplotlib config directory
Set matplotlib qt backend
Avoid import of matplotlib QT lib if QT is not installed
add optional + default in pyx docstring
Use None instead of 'none' for qt backend
Fix setting of QT_API environment variable
Fix python 3 print statement in example script
Fix window size of sub-pixel corner detection
Fix matching example script
Merge pull request #571 from ahojnnes/travis-fix

Fix: Use None instead of 'none' for qt_api (fix Travis error), set matplotlib backend
  also use python 3 print() in example.
Merge pull request #572 from sciunto/docandco

add optional + default in pyx docstring
Modified 'denoise_bilateral':\n1) check that image max value is not zero to avoid segmentation fault.\n2) initialize color_lut after sigma_range has been checked.
Deported variable initialization after the cdef block to allow verifications.
Reduce code duplication in test_radon_transform

Although the line count is increased by these changes, future tests can
be written in fewer lines.
PEP8 fixes for test_radon_transform
Merge pull request #578 from josteinbf/radon-test-refactor

Reduce code duplication in tests for transform.radon_transform
Moved image conversion after the verification of the max_value
Merge pull request #576 from alexis-mignon/master

Bugs in filter.denoise_biltateral.