Decompressed Stream Support

[fairingrey]

Description

This PR seeks to add support for decompressing streams of encoded bytes under each of the encoding algorithms used.

This is the current progress:

• Brotli
• Deflate
• Gzip
• Zlib

Motivation and Context

Coming up with a standard pattern of decompressing encoded streams that the library already provides would be valuable for various use cases.

It would also unblock progress on http-rs/tide#194.

How Has This Been Tested?

Tests are added.

• Brotli
• Deflate
• Gzip
• Zlib

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[fairingrey]

r? @Nemo157

[Nemo157]

Overall looks good, just a couple of small issues in the flate compression.

[fairingrey]

@Nemo157 I think I'm ready for another review.

EDIT: Well, I could write more tests, actually (and probably ones that don't depend on implementations native to this crate), but I'll ask more about them later.

[fairingrey]

A remark on using Bytes::extend_from_slice here:

https://github.com/rustasync/async-compression-rs/blob/014a2e101d9b044517399d9006872d84efb6c621/src/stream/gzip.rs#L255

The only time(s) this is reached is when the input is too small be read as data, as the footer will always take up 8 bytes, and the check here:

https://github.com/rustasync/async-compression-rs/blob/014a2e101d9b044517399d9006872d84efb6c621/src/stream/gzip.rs#L265

Prevents the footer from being read as data. So I think this is the best I can get it without it freaking out on any odd/malformed data.

Let's go with one more review, and I think this should be good? @Nemo157

[fairingrey]

Oh right, I forgot the inner stream can be pending. I'll fix it up right now.

[Nemo157]

Awesome, now I'll rebase the proptest branch on this and see if I can break it 😈