BUG: Take the absolute difference between times when determining the correct tick interval
DEP : update six minimum version

 turns out we really need version 1.4 or better

fixes #3538
TST: Added test for inverted limit with autodatelocator
STY/TST: pep8 fixes for test_dates
Merge pull request #3524 from cimarronm/autodatelocaltor_3522

FIX : Bug in AutoDateLocator when dates are in reverse order
Fix warning in lines.py
Indent correctly in mlab
silence warnings in art3d
Fix warnings in cbook

Deprecation examples and a line continuation
Fix warnings in _axes

Render other args of title better, etc
fix rendering of warnings in mlab
Improve rendering of title docs
Merge pull request #3539 from tacaswell/six_fix

DEP : update six minimum version
docstring in trirefine
Merge pull request #3548 from jenshnielsen/autodoc_fixes

Silence some Sphinx warnings by rewriting docstrings.
Merge pull request #3545 from mdehoon/setfont_informative_error_message

MNT : Provide an informative error message if something goes wrong in setfont
DOC: Fixed comment documentation to match with code on timer interval set to 100 ms
Merge pull request #3555 from cimarronm/timer_example_docfix

MNT : Typo in comment documentation for example timers.py
Remove backticks around None. This is not a ref
Fix formatting in docstring for dates