Move tests and support utilities to sub crates. (#268)

These crates will not be published to crates.io, but moving them allows
`tower-h2` to also depend on the test utilities.

tests/h2-support/src/lib.rs

@@ -0,0 +1,36 @@
+//! Utilities to support tests.
+
+pub extern crate bytes;
+pub extern crate env_logger;
+#[macro_use]
+pub extern crate futures;
+pub extern crate h2;
+pub extern crate http;
+pub extern crate string;
+#[macro_use]
+pub extern crate tokio_io;
+
+#[macro_use]
+mod assert;
+
+pub mod raw;
+
+pub mod frames;
+pub mod prelude;
+pub mod mock;
+pub mod mock_io;
+pub mod notify;
+pub mod util;
+
+mod future_ext;
+
+pub use future_ext::{FutureExt, Unwrap};
+
+pub type WindowSize = usize;
+pub const DEFAULT_WINDOW_SIZE: WindowSize = (1 << 16) - 1;
+
+// This is our test Codec type
+pub type Codec<T> = h2::Codec<T, ::std::io::Cursor<::bytes::Bytes>>;
+
+// This is the frame type that is sent
+pub type SendFrame = h2::frame::Frame<::std::io::Cursor<::bytes::Bytes>>;