tools/compression: add DeflateEncoder and helpers

implements a deflate encoder that can compress anything that implements
AsyncRead + Unpin into a file with the helper 'compress'

if the inner type is a Stream, it implements Stream itself, this way
some streaming data can be streamed compressed

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

Cargo.toml

@@ -29,6 +29,7 @@ bitflags = "1.2.1"
 bytes = "1.0"
 crc32fast = "1"
 endian_trait = { version = "0.6", features = ["arrays"] }
+flate2 = "1.0"
 anyhow = "1.0"
 futures = "0.3"
 h2 = { version = "0.3", features = [ "stream" ] }