split facade modules into separate files (#665)

src/prelude.rs

@@ -0,0 +1,54 @@
+//! A "prelude" for users of the `tokio` crate.
+//!
+//! This prelude is similar to the standard library's prelude in that you'll
+//! almost always want to import its entire contents, but unlike the standard
+//! library's prelude you'll have to do so manually:
+//!
+//! ```
+//! use tokio::prelude::*;
+//! ```
+//!
+//! The prelude may grow over time as additional items see ubiquitous use.
+
+pub use tokio_io::{
+    AsyncRead,
+    AsyncWrite,
+};
+
+pub use util::{
+    FutureExt,
+    StreamExt,
+};
+
+pub use ::std::io::{
+    Read,
+    Write,
+};
+
+pub use futures::{
+    Future,
+    future,
+    Stream,
+    stream,
+    Sink,
+    IntoFuture,
+    Async,
+    AsyncSink,
+    Poll,
+    task,
+};
+
+#[cfg(feature = "async-await-preview")]
+#[doc(inline)]
+pub use tokio_async_await::{
+    io::{
+        AsyncReadExt,
+        AsyncWriteExt,
+    },
+    sink::{
+        SinkExt,
+    },
+    stream::{
+        StreamExt as StreamAsyncExt,
+    },
+};