REL: set version to 0.19.0 (with Python 3.4-3.9 support)

REL: set version to 0.18.0

REL: add 0.17.0 release notes and set version to 0.17.0

REL: add 0.16.0 release notes and set version to 0.16.0

REL: set version to 0.15.0 and add release notes.