ResidentMario/geoplot: 0.5.0 maintenance release

This maintenance release includes the follows breaking changes:

• The minimum Python version has been raised to 3.7, as Python 3.6 has now reached EOL (#270).
• The handling of certain parameters (namely: legend, cmap, and hue) to geoplot.kdeplot has been changed. Previously these parameters were interpreted by geoplot directly. Now they are simply passed down to the underlying seaborn.kdeplot instance (#271, #272).

This maintenance release includes the following non-breaking changes:

• Removed the deprecation warning for the long-removed k parameter (#273).
• Fixed various deprecation notices in underlying libraries (#268, #269).
• Miscellaneous minor fixes in code and docs.