Reader fror zst compressed files

[likeawizard]

1. Find a golang library that implements zst decompression and allows to create a reader from it
2. Examine existing handling of bzip2 implementation parser.go:38
3. Create a more universal ReaderFactory
   1. It should take a file path or FileInfo parameter and return the appropriate Reader and/or error
   2. It should support plain .pgn files, bzip2 and zst
   3. If possible try to get/estimate total data amount for progress estimate