libtextstyle: be sure to have ostream_printf and hyperlink support

Older versions of libtextstyle do not support them, rule them out.

Reported by Lars Wendler
https://lists.gnu.org/r/bug-bison/2020-07/msg00030.html

and by Arnold Robbins
https://lists.gnu.org/r/bug-bison/2020-07/msg00041.html and
https://lists.gnu.org/mailman/private/gawk-devel/2020-July/003988.html

and by Nelson H. F. Beebe
https://lists.gnu.org/mailman/private/gawk-devel/2020-July/003993.html

With support from Bruno Haible in gnulib
https://lists.gnu.org/r/bug-gnulib/2020-08/msg00000.html
thread starting at
https://lists.gnu.org/r/bug-gnulib/2020-07/msg00148.html

* configure.ac: Require libtextstyle 0.20.5.
* gnulib: Update.

lib/.gitignore

@@ -192,8 +192,6 @@
 /localcharset.h
 /locale.h
 /locale.in.h
-/localtime-buffer.c
-/localtime-buffer.h
 /lstat.c
 /malloc.c
 /malloca.c