* configure.ac (AC_INIT): Update version info for release.
(OCTAVE_MINOR_VERSION): Set to 1.
(OCTAVE_PATCH_VERSION): Set to 0.
(OCTAVE_RELEASE_DATE): Set to 2019-02-23.

* org.octave.Octave.appdata.xml: Add 5.1.0 to the list of version
numbers and release dates.