v0.9.2  November 2017:  First version to be published on PyPI
v0.9.3  November 2017:  Some optimisations, without any behaviour changes.
        Calculating the likelihood is now significantly faster for large
        interpolated grids and where flux upper bounds aren't used.  This was
        achieved by avoiding using intermediate arrays in the calculations.
        Marginalising PDFs is now faster for grids with 4 or more dimensions
        due to the use of a cache.
v0.9.4  January 2018:  Allowed the use of linear or cubic interpolation when
        interpolating input model grid flux arrays, with the new keyword option
        "interp_order".  Previously only linear interpolation was available.
v0.9.5  Jan-Feb 2018:  Convert print statements to use python logging, and add
        the "verbosity" argument to NB_Model.__call__.  Some minor changes to
        better support unicode in python 2, and include metadata in .pdf files.
v0.9.6  Mar 2018:  Add "likelihood_lines" keyword option.  In the "best model"
        tables, the "Delta_(SDs)" field was renamed to "Resid_Stds" and now
        provides "(obs - model)/sigma" instead of "(model - obs)/sigma".  The
        resolution of output images was increased.
v0.9.7  Added citation info for the NebulaBayes paper to the documentation and
        clarified that the cubic interpolation option is experimental. The PyPI
        "Developement status" was changed from "Beta" to "Production/Stable".
