v0.21.1 Final

This is a minor bug-fix release in the 0.21.x series and includes some small
regression fixes, bug fixes and performance improvements. We recommend that all
users upgrade to this version.

Highlights include:

• Temporarily restore matplotlib datetime plotting functionality. This should
  resolve issues for users who relied implicitly on pandas to plot datetimes
  with matplotlib. See here
• Improvements to the Parquet IO functions introduced in 0.21.0. See
  here

See the v0.21.1 Whatsnew overview for an extensive list
of all the changes for 0.21.1.