Lagrange [release]

Bumped version to 1.7.3; updated release notes

Tue Oct 19 11:26:12 2021 +0300

 CMakeLists.txt                      |  2 +-
 res/about/version.gmi               |  5 +++++
 res/fi.skyjake.Lagrange.appdata.xml | 20 ++++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)