Add support for `-ps` `s = sextant blocks`

[acxz]

Currently we support half blocks and quarter blocks, it would be amazing if we can add support for sextant blocks to provide higher resolution.

    " ", "🬀", "🬁", "🬃", "🬇", "🬏", "🬞", "🬂", // 0..7
    "🬄", "🬈", "🬐", "🬟", "🬅", "🬉", "🬑", "🬠", // 8..15
    "🬋", "🬓", "🬢", "🬖", "🬦", "🬭", "🬆", "🬊", // 16..23
    "🬒", "🬡", "🬌", "▌", "🬣", "🬗", "🬧", "🬍", // 24..31

    "█", "🬻", "🬺", "🬹", "🬸", "🬷", "🬶", "🬵",
    "🬴", "🬳", "🬲", "🬱", "🬰", "🬯", "🬮", "🬭",
    "🬬", "🬫", "🬪", "🬩", "🬨", "▐", "🬧", "🬦",
    "🬥", "🬤", "🬣", "🬢", "🬡", "🬠", "🬟", "🬞",
    "🬝", "🬜", "🬛", "🬚", "🬙", "🬘", "🬗", "🬖",
    "🬕", "🬔", "▌", "🬓", "🬒", "🬑", "🬐", "🬏",
    "🬎", "🬍", "🬌", "🬋", "🬊", "🬉", "🬈", "🬇",
    "🬆", "🬅", "🬄", "🬃", "🬂", "🬁", "🬀", " ",

This is inspiration from how notcurses renders, see here for relevant code.

Another more drastic idea could be to completely replace the backend rendering of timg with notcurses. And essentially have timg be a media player frontend around notcurses.

As a workaround to this issue, users can use chafa instead.