Merge branch 'maint'

Merge branch 'maint'

* maint:
  docs: '.txi' and '.texinfo' extensions are deprecated
  NEWS: document recent documentation improvements
  docs: more precise cross reference
  docs: 'dist-shar' and 'dist-tarZ' are obsolescent today
  docs: improve documentation of 'dist-*' targets slightly
  docs: make even clearer 'dist-gzip' is the default.
  docs: document 'dist-xz' together with the other 'dist-*' options
  docs: 'no-define' option and AM_INIT_AUTOMAKE three-args usage: fixlets
  warn: correct broken hyperlink in warning message