nipy/nibabel: 3.2.1

Most work on NiBabel so far has been by Matthew Brett (MB), Chris Markiewicz (CM), Michael Hanke (MH), Marc-Alexandre Côté (MC), Ben Cipollini (BC), Paul McCarthy (PM), Chris Cheng (CC), Yaroslav Halchenko (YOH), Satra Ghosh (SG), Eric Larson (EL), Demian Wassermann, Stephan Gerhard and Ross Markello (RM). References like "pr/298" refer to github pull request numbers. 3.2.1 (Saturday 28 November 2020) Bug fix release in the 3.2.x series. Maintenance Drop references to builtin types in Numpy namespace like <code>np.float</code> (pr/964) (EL, reviewed by CM) Ensure compatibility with Python 3.9 (pr/963) (CM)