Substituted comparisons '==None' with 'is None'
Changed a few more comparisons to 'is None'
Bugfix in rename_layer(): block_name_list property wasn't being updated
Added rename_column() method
Minor modification to read()- to handle keyword lines with extra comments on them
Bugfix in refine(): was failing when refining 2-D grids
Experimental version of slice_plot() with column_axis and layer_axis parameters, giving second axes with column and layer names
Rewrote column_axis and layer_axis features in slice_plot(), so that they substitute for default coordinate axes (instead of creating new additional axes)
Bugfix in column_values(): atmosphere block name wasn't always being determined correctly
Added PyTOUGH user guide to git repository, and altered documentation to reflect this (prompted by Github deprecating the Downloads section on the website)
Documentation update
Version 1.3.6