[feature] zlib, raw deflate, full deflate streams

[sstadick]

This PR reworks a lot of the internals of gzp. There is now one generic "engine" that operates over anything that implements FormatSpec. This now include Gzip, Zlib, Raw Deflate, and Snap.

Additionally, instead of writing many gzip blocks with their own headers and no overlapping dicts, this now behaves like pigz and writes a single stream that uses the last 32K of the previous block as the dict for the next block.

There are two features that still need to be implemented in future PRs:

• Add the ability to set more metadata in the gzip and zlib headers
• Drop the libz_sys req for zlib when using the rust backend and find an andler crate that has a combine method.