ENH: Look for styles in ~/.config/matplotlib/stylelib for XDG compliance
PEP8 removed trailing whitespace
use matplotlib._get_configdir() rather than manually setting path to config dir
Merge branch 'master' of github.com:matplotlib/matplotlib into styles_XDG_compliance
Merge pull request #2720 from alimuldal/styles_XDG_compliance

Look for user-specified styles in ~/.config/matplotlib/stylelib