Change in default font

The default font used by matplotlib in text has been changed to DejaVu Sans and

DejaVu Serif for the sans-serif and serif families, respectively. The DejaVu

font family is based on the previous matplotlib default --Bitstream Vera-- but

include a much wider range of characters.

The default mathtext fonts has been changed from Computer Modern to the DejaVu

family to maintain consistency with regular text. Two new options for the

``mathtext.fontset`` configuration parameter have been added: ``dejavusans``

(default) and ``dejavuserif``. Both of these options use DejaVu glyphs whenever

possible and fall back to STIX symbols when a glyph is not found in DejaVu.