Improvements to anchored_artists.AnchoredSizeBar

Fix: color argument was not setting the color of the textlabel
Add: setting the font-size through the fontsize argument
Add fontprop parameter to anchored_artists.AnchoredSizeBar

Removed the old fontsize parameter.
And fix: some typos in the example in the docstring
Modify AnchoredSizeBar: change fontprops argument to fontproperties
Merge pull request #7 from magnunor/pelson_anchored_sizebar_fontprop

Modify AnchoredSizeBar: change fontprops argument to fontproperties
Merge pull request #2712 from pelson/anchored_sizebar_fontprop

Anchored sizebar fontprop