A dead node used by text-layout to draw strings.
It supports the node interface and the mask interface.
void vcl_string_init (struct vcl_string *obj, const char *string,
uns charmap, int font_id, real font_size,
const struct geom_rectangle *bbox)
string is a string of glyph codes (in UTF-8),
charmap and font_id are fontlib values specifying the font and
interpretation of glyph codes from string. font_size is the font size and bbox is
the bounding box of the string, both in local coordinates.