doc: use UTF-8 encoding * doc/gnulib.texi: Use ‘@documentencoding UTF-8’. Partly this is because there are a few UTF-8 characters in the .texi files and there seems little point nowadays to @U-ifiying them. And partly it is so that the .info output uses nicer UTF-8 characters, e.g., it single-quotes ‘like this’ instead of 'like this'.