Seezee

A seekable zstd compressed buffer.

This is very similar to the seekable format extension, with some small differences:

• The resulting buffer is not a valid zstd file, and cannot be handled directly by other zstd decompression tools.
• All frames have the same (uncompressed) size, so there is no need to store than and binary search.
• Frames are stored without the zstd magic, saving a few bytes.

I might add support for an embedded dictionary in the future.