Constant ptree::print_config::UTF_CHARS_DOUBLE

pub const UTF_CHARS_DOUBLE: StaticIndentChars = StaticIndentChars{down_and_right: "╠",
                  down: "║",
                  turn_right: "╚",
                  right: "═",
                  empty: " ",}

UTF-8 indentation characters, using double box-drawing characters