Respect user-input legend fontsize (fix #331)

Author: lukelbd

WHATSNEW.rst

@@ -235,6 +235,8 @@ Bug fixes
   max of `levels` when passed to `~proplot.colors.DiscreteNorm` (:commit:`e9ed16c1`).
 * Fix issue where unevenly-spaced `levels` combined with
   `~proplot.colors.DiscreteColormap` incorrectly samples the color list (:issue:`299`).
+* Fix issue where `~proplot.axes.Axes.legend` ignores the user-input
+  `fontsize` (:issue:`331`).
 * Fix issue where setting :rcraw:`legend.facecolor` or :rcraw:`legend.edgecolor` to
   ``'inherit'`` (or passing as keyword argument) raises error (:issue:`298`).
 * Fix issue where settings :rcraw:`grid.pad` and :rcraw:`grid.labelpad` and settings

proplot/axes/base.py

@@ -1199,7 +1199,7 @@ def _add_legend(
         ncol = _not_none(ncols=ncols, ncol=ncol)
         order = _not_none(order, 'C')
         frameon = _not_none(frame=frame, frameon=frameon, default=rc['legend.frameon'])
-        fontsize = _not_none(kwargs.pop('fontsize', None), rc['legend.fontsize'])
+        fontsize = _not_none(fontsize, rc['legend.fontsize'])
         titlefontsize = _not_none(
             title_fontsize=kwargs.pop('title_fontsize', None),
             titlefontsize=titlefontsize,