libtextstyle: styled-ostream: Add hyperlink support.
* libtextstyle/gnulib-local/lib/styled-ostream.oo.h (struct styled_ostream): Add
methods get_hyperlink_ref, get_hyperlink_id, set_hyperlink.
* libtextstyle/gnulib-local/lib/term-styled-ostream.oo.c
(term_styled_ostream::get_hyperlink_ref, term_styled_ostream::get_hyperlink_id,
term_styled_ostream::set_hyperlink): New functions.
* libtextstyle/gnulib-local/lib/html-styled-ostream.oo.c
(struct html_styled_ostream): Add field hyperlink_id.
(html_styled_ostream::free): Free the hyperlink_id field.
(html_styled_ostream::get_hyperlink_ref, html_styled_ostream::get_hyperlink_id,
html_styled_ostream::set_hyperlink): New functions.
(html_styled_ostream_create): Initialize the hyperlink_id field.
* libtextstyle/gnulib-local/lib/noop-styled-ostream.oo.c
(struct noop_styled_ostream): Add fields hyperlink_ref, hyperlink_id.
(noop_styled_ostream::free): Free the hyperlink_ref and hyperlink_id fields.
(noop_styled_ostream::get_hyperlink_ref, noop_styled_ostream::get_hyperlink_id,
noop_styled_ostream::set_hyperlink): New functions.
(noop_styled_ostream_create): Initialize the hyperlink_ref and hyperlink_id
fields.
* libtextstyle/lib/textstyle.h (styled_ostream_get_hyperlink_ref,
styled_ostream_get_hyperlink_id, styled_ostream_set_hyperlink,
term_styled_ostream_get_hyperlink_ref, term_styled_ostream_get_hyperlink_id,
term_styled_ostream_set_hyperlink, html_styled_ostream_get_hyperlink_ref,
html_styled_ostream_get_hyperlink_id, html_styled_ostream_set_hyperlink,
noop_styled_ostream_get_hyperlink_ref, noop_styled_ostream_get_hyperlink_id,
noop_styled_ostream_set_hyperlink): New declarations.
* libtextstyle/adhoc-tests/hello.c (main): Invoke styled_ostream_set_hyperlink.
