[New feature] Compression support (BEP56)

[Alexander Ivanov]

As from bittorrent/bittorrent.org#124:

When Bittorrent was created, compression algorithms was slow and expensive, so user must have share uncompressed files or compress it manually to ZIP/RAR/etc.

Now people still share files in .zip archives (or even in .rar, yikes!), which takes additional space and needs to be uncompressed to somewhere. Instead, why shouldn't we compress torrent pieces on-the-fly?

We have fast compression algorithms like LZO, LZ4, Snappy and Zstandard, which allows torrenting uncompressed files directly, yet not sacrifing upload speed like if it was pre-compressed.

I suggest standardizing and implementing compression as per bittorrent/bittorrent.org#125