Add support for optional Zstd seekable format

Seekable format allows the generated compressed files to be random-access accesible.

https://github.com/facebook/zstd/tree/dev/contrib/seekable_format

I belive Zstd supports this format in the standard, but its up to the compressor to use it.

I dont know how extensive the changes needs to be to support it, i know it requires to use independient blocks and create the jump table.