libtextstyle: Support for terminal types with 256 colors.
* gnulib-local/lib/term-ostream.oo.c (term_ostream_create): Accept all $TERM
values that end in -16color or -256 color (such as Eterm-256color,
mlterm-256color, or putty-256color).
* libtextstyle/NEWS: Mention the change.
