REL: v3.1.3

This is the final planned release of the 3.1.x series.

This release contains several critical bug-fixes:

 - suppress a warning with Pandas 1.0
 - support pillow >= 7
 - support dateutils >= 2.8.1
 - prevent an infinite recursion
 - do not clobber non-python registered signal handler
 - fix path intersection computation with 0 length segments
 - fix performance regression in draw_idle
 - several minor bugs