cli: add option to output locations to gpx files

tox.ini

@@ -85,6 +85,7 @@ allowlist_externals = cat
 commands =
     pip install -e .[testing,optional]
     pip install orgparse # used it core.orgmode?
+    pip install gpxpy # for hpi query --output gpx
 
     {envpython} -m mypy --install-types --non-interactive \
                     -p my.core \