#669 ZST support

[Chaython Meredith]

Peazip still requires writing zst as tarball.
Meanwhile 7zip-zstd https://github.com/mcmilk/7-Zip-zstd Just writes as .7z
Peazip poorly handles zst writing as a zst, then I open it, the tarball is inside and its a second clickthrough, if i try to drag files into it, it writes it to the temporary windows folder, not the actual archive.

[Giorgio Tani]

Hi, PeaZip for Windows uses McMilk Open Source codecs for 7z.
From Advanced tab of archiving screen you can select Brotli, FLZMA2, Lizard, LZ4, LZ5, and Zstd methods of compression for .7z archives (those methods are not part of "vanilla" 7-Zip implementation).
Archives created in that way are fully compatible with ones created with McMilk's 7-Zip fork.

Zstandard itself is a pure compression format, and does not provide the ability to create archives containing multiple files and folders, this is the reason why "plain" zstd compression requires creating a tar archive before compression, in case of multiple input items.
Please note that even if this is less handy than creating a zstd-compressed 7z archive, it may be preferred on non-Windows systems as tar archive format is better suited to save/backup Unix-like specific filesystem characteristics which are out of the scope of a generic, platform independent format as 7z.