dot: add option 'g'

* spot/twaalgos/dot.cc: Implement support for hidding labels.
* tests/core/readsave.test: Test it.
* bin/common_aoutput.cc: Add --help text.
* NEWS: Mention it.
23 jobs for next in 520 minutes and 31 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #37835
alpine-gcc

00:27:34

passed #37836
arch-clang

00:48:12

passed #37857
arch-gcc-glibcxxdebug

00:53:43

passed #37869
debian-gcc-snapshot

01:48:14

passed #37870
debian-stable-gcc

00:42:02

passed #37855
debian-unstable-gcc-coverage

00:46:14

88.6%
passed #37840
debpkg-stable

02:35:12

passed #37874
debpkg-unstable

03:19:55

passed #37838
mingw-shared

00:14:09

passed #37839
mingw-static

00:12:23

passed #37871
rpm-pkg

00:48:16

failed #37837
arch-gcc-glibcxxdebug

00:14:52

failed #37834
debian-gcc-snapshot

00:14:51

failed #37856
debian-gcc-snapshot

00:11:50

failed #37832
debian-stable-gcc

00:00:15

failed #37854
debian-stable-gcc

00:16:23

failed #37833
debian-unstable-gcc-coverage

00:00:14

failed #37841
debpkg-unstable

01:59:48

failed #37853
debpkg-unstable

02:11:28

failed #37858
rpm-pkg

00:12:11

failed #37842
rpm-pkg

00:15:47

 
  Publish
passed #37843
dput
publish-rpm

00:00:30

passed #37844
dput
publish-unstable

00:03:24