[glibmm] (13 commits) Non-fast-forward update to branch wip/dboles/ustring-sprintf

[Daniel Boles <dboles src gnome org>]

The branch 'wip/dboles/ustring-sprintf' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  6bfcb31... ustring: Add sprintf(), wrapping g_strdup_printf()

Commits added to the branch:

  fbe267d... ustring: Use C++17 fold expr. instead of recursion (*)
  a485da1... tests/glibmm_ustring_format: Test output, iomanips (*)
  f6e3298... ustring: Make 1 Stringify member const like others (*)
  c4de725... ustring: Avoid un(necessary|clear) ptr @ Stringify (*)
  3b3d656... ustring: Remove useless alternative Stringify ctor (*)
  25846ce... tests/glibmm_ustring_format: Fix non-English langs (*)
  9a5acb6... tools/test_scripts/testheaders.sh: Require C++17 (*)
  410e03e... Merge branch 'wip/dboles/ustring_format_fold_and_test' into (*)
  f4fea71... Add tools/gen_scripts/generate_all.sh (*)
  5a20ffa... Glib, Gio: Regenerate .defs and docs.xml files (*)
  906cb65... Change the ABI to glibmm-2.60 (*)
  2013b71... 2.59.1 (*)
  c1c5c4e... ustring: Add sprintf(), wrapping g_strdup_printf()

(*) This commit already existed in another branch; no separate mail sent