Merge pull request SciTools#2059 from dopplershift/backport-2057

Backports for 0.20.x

Merge pull request SciTools#1969 from greglucas/v0.20-pcolormesh

Backport recent master commits to v0.20.x

REL: v0.20.1

This is the first bugfix of the v0.20.x series.

See the list of bugfixes on the milestone:
https://github.com/SciTools/cartopy/milestone/31?closed=1

Merge pull request SciTools#1867 from greglucas/doc-whatsnew-0.20

DOC: whats new v0.20

Merge pull request SciTools#1769 from greglucas/sdist-work

FIX: Adding build_ext call to setup.py on release

Merge pull request SciTools#1703 from greglucas/whatsnew_0.19

DOC: Adding release notes for v0.19

First release candidate for Cartopy v0.19.0.

Cartopy 0.18.0

Major changes include:

* Support for building against Proj 6.
* Support for Python 3.7 and 3.8.
* Support for Matplotlib 3.2 and 3.3.
* Support for labelling gridlines on all projections.
* Support for labelling gridlines within plot boundaries instead of
  edges.
* Support for labelling of contours.

and many others.

There are several bug fixes as well. See [the
milestone](https://github.com/SciTools/cartopy/milestone/25?closed=1)
for more information.

Cartopy 0.18.0 release candidate 1

Major changes include:

* Support for building against Proj 6.
* Support for Python 3.7 and 3.8.
* Support for Matplotlib 3.2 and 3.3.
* Support for labelling gridlines on all projections.
* Support for labelling gridlines within plot boundaries instead of
  edges.
* Support for labelling of contours.

and many others.

There are several bug fixes as well. See [the
milestone](https://github.com/SciTools/cartopy/milestone/25?closed=1)
for more information.

Cartopy 0.18.0 beta 2

Major changes include:

* Support for building against Proj 6.
* Support for Python 3.7 and 3.8.
* Support for Matplotlib 3.2 and 3.3.
* Support for labelling gridlines on all projections.
* Support for labelling gridlines within plot boundaries instead of
  edges.
* Support for labelling of contours.

and many others.

There are several bug fixes as well. See [the
milestone](https://github.com/SciTools/cartopy/milestone/25?closed=1)
for more information.