rutrackerer -- index and search through Rutracker's XML

Rutracker is located now beneath Cloudflare, so you can not use it
anymore without compromising your computer with required downloadable
JavaScript programs.

But you can get its full contents (without comments) in XML form from
https://rutracker.org/forum/viewtopic.php?t=5591249

    $ curl "http://api.rutracker.org/v1/get_tor_hash?by=topic_id&val=5591249"
    {"result":{"5591249":"FE63F7FA266E8F3F812FF637EB9025413CB58D51"}}
    # http://api.rutracker.org/v1/get_topic_id?by=hash&val=FE63F7FA266E8F3F812FF637EB9025413CB58D51
    $ aria2c "magnet:?xt=urn:btih:FE63F7FA266E8F3F812FF637EB9025413CB58D51"

It is recommended to recompress it with Zstandard, to save the space and
quickly feed in further commands. That XML is huge, so you can get some
troubles searching in it quickly. So here are the indexer, that extracts
titles, sizes, hashes and XML offsets:

    $ cmd/index < rutracker-XXX.xml | cmd/repack > rutracker.gob

On my computer that takes seven minutes.

After that, you can search the desired title like that:

    $ cmd/search -i "borknagar .* origin" < rutracker.gob
    (Avantgarde/Folk/Black Metal) Borknagar - Коллекция (6 Original CD) [...]
            2011-06-13T12:05:00 2.1 GiB 10625776348
            https://rutracker.org/forum/viewtopic.php?t=3571053
            magnet:?xt=urn:btih:69A167FC69640304D0EF410ADDFBED80C1156989
    (Rock, Acoustic) [LP] [24/96] Borknagar - Origin - 2018 (2006), FLAC
            2021-04-14T10:25:00 762 MiB 22050441855
            https://rutracker.org/forum/viewtopic.php?t=6040594
            magnet:?xt=urn:btih:E562633975C28E3CC385F7AD7446D53B3DD883D1

Titles are fed into external "grep" command's stdin and all command
line arguments are also proxied as is. GNU Grep is really pretty fast at
that job.

Optionally you can view corresponding contents from that XML, by
providing the offset:

    $ zstd -d < rutracker-XXX.xml.zst | cmd/show 22050441855
     <title>(Rock, Acoustic) [LP] [24/96] Borknagar – Origin - 2018 (2006) [...]
     <torrent hash="E562633975C28E3CC385F7AD7446D53B3DD883D1" tracker_id="2"/>
     <forum id="1756">Hi-Res форматы, оцифровки - Оцифровки с аналоговых [...]
    [b]Жанр[/b]: Rock, Acoustic
    [b]Носитель[/b]: LP
    [b]Год выпуска[/b]: 2018 (2006)
    [b]Лейбл[/b]: Cosmic Key Creations &#8206;– CKC041
    [b]Страна-производитель[/b]: Netherlands
    [b]Аудио кодек[/b]: FLAC
    [b]Тип рипа[/b]: tracks
    [b]Формат записи[/b]: 24/96
    [b]Формат раздачи[/b]: 24/96
    [b]Продолжительность[/b]: 00:35:32
    [...]