Merge remote-tracking branch 'upstream/v2.0.x'

* upstream/v2.0.x:
  Move v2.0.x branch into development mode.
  Release of iris v2.0.0 🎉
  Improved the pip installability of scitools-iris. (SciTools#2956)
  Add a general zenodo link to the readme. (SciTools#2955)
  No docs are better than wrong docs on dask
  DOC: lazy data docstring made clearer (SciTools#2947)
  Remove gdal from 'all' to 'extensions' depedency group.
  Tweaked what's new, bumped version string, and updated the MANIFEST for pypi.