Release v2.0.0 - Drop Python 2.7 support

Release v1.22.0 (pytest-dev#226)

New release v1.21.1 (pytest-dev#211)

v.1.21.0 (pytest-dev#209)

Fix version number and release date in notes

Update release notes for v1.19.0

Update release notes for v1.18.0

Update release notes for v1.17.0

Update release notes for v1.16.1

Update release notes for v1.16.0