Add async-I/O support to the crate

* Add an optional `tokio` feature to enable
* Add `AsyncRead` and `AsyncWrite` trait implementations where appropriate.
* Add a few misc methods for appropriate use with async
* Avoid use of methods like `write_all` which aren't async-compatible.

Currently the gzip `Read`-based streams do not implement `AsyncRead` due to the
necessity for a large implementation overhaul if doing so.

Closes rust-lang#91
Closes rust-lang#92
Closes rust-lang#93

.travis.yml

@@ -11,6 +11,8 @@ script:
   - cargo build --verbose
   - cargo test --verbose
   - cargo test --verbose --features zlib
+  - cargo test --verbose --features tokio
+  - cargo test --verbose --features 'tokio zlib'
   - cargo test --verbose --features zlib --no-default-features
   - cargo clean && cargo build
   - rustdoc --test README.md -L target/debug -L target/debug/deps

Cargo.toml

@@ -22,11 +22,15 @@ streams.
 libc = "0.2"
 miniz-sys = { path = "miniz-sys", version = "0.1.7", optional = true }
 libz-sys = { version = "1.0", optional = true }
+tokio-io = { version = "0.1", optional = true }
+futures = { version = "0.1", optional = true }
 
 [dev-dependencies]
 rand = "0.3"
 quickcheck = { version = "0.4", default-features = false }
+tokio-core = "0.1"
 
 [features]
 default = ["miniz-sys"]
 zlib = ["libz-sys"]
+tokio = ["tokio-io", "futures"]

appveyor.yml

@@ -15,3 +15,4 @@ build: false
 
 test_script:
   - cargo test --verbose --target %TARGET%
+  - cargo test --verbose --target %TARGET% --features tokio