Splitted the axes module into smaller chunks
FIX process_plot_format is not in the axes module anymore
ENH now can run the tests on triangulation without the test runner
Documented the changes
DOC the refactoring of the axes module is now mentionned in the API_changes.rst file
ENH shuffled around some extra methods between Axes and _AxesBase
FIX importing _string_to_bool from the wrong module
DOC - added the differences between the axes module namespace before and after
Merge pull request #1931 from NelleV/axes_module

[SPRINT] Refactored the axes module to split it in smaller chunks.