add svg logo icon

icon created using the logo example https://matplotlib.org/gallery/misc/logos2.html
and parameters

make_logo(height_px=360, lw_bars=1.5, lw_grid=1.0, lw_border=3.0,
           rgrid=[1, 3, 5, 7], with_text=False)
plt.savefig('matplotlib-icon.svg')

and compressed via https://vecta.io/nano (compression level 5).

Author: timhoffm