Post split-off. As per https://github.com/bitcoin/bitcoin/blob/master/doc/release-process.md#before-every-major-release and issue #16996.
Note: after split-off, the same changes should be made on the new 0.19.0 release branch, with also these additional changes to both files (configure.ac and build_msvc/bitcoin_config.h):
- set
CLIENT_VERSION_REVISIONto0 - set
CLIENT_VERSION_IS_RELEASEtotrue
The second commit resets the release notes after branch-off and proposes a few improvements.