v0.1.x lint fix, MSRV 1.28.0 updates (#1451)

* use dyn Trait syntax where appropriate

recent rust nightly started warning that not using `dyn` was
deprecated. This requires MSRV 1.27.0+.

* rustfmt fallout from dyn additions

* stop explicit allow of rust_2018_idioms

* more dyn Trait syntax

* drop tokio-macros from 0.1.x workspace

Since tokio-macros specifies an edition=2018, we would otherwise
require MSRV 1.31.0 to build/test it. And tokio-macros isn't used with
tokio 0.1.x.

* reactor: narrow tokio-io-pool dev dep to 0.1.4

Since 0.1.5-6 is now a edition=2018 crate, which has effective MSRV
1.31.0.

* narrow tempfile dev-dep to avoid MSRV bump

tempfile 3.1.0 pulls in rand 0.7.0 and is MSRV 1.32.0

* narrow flate2 dev-dep to avoid MSRV bump

flate2 1.0.10-11 have MSRV 1.34.0.

github refs: alexcrichton/flate2-rs#207

* fs: drop deprecated tempdir crate use in tests

In particular because it pulls in old rand duplicates. Replace use
with tempfile::tempdir() which has been available since tempfile
3.0.0.

backport-of: #1312

* increase CI MSRV to 1.28.0

tokio-io/src/lib.rs

@@ -21,10 +21,10 @@ use std::io as std_io;
 use futures::{Future, Stream};
 
 /// A convenience typedef around a `Future` whose error component is `io::Error`
-pub type IoFuture<T> = Box<Future<Item = T, Error = std_io::Error> + Send>;
+pub type IoFuture<T> = Box<dyn Future<Item = T, Error = std_io::Error> + Send>;
 
 /// A convenience typedef around a `Stream` whose error component is `io::Error`
-pub type IoStream<T> = Box<Stream<Item = T, Error = std_io::Error> + Send>;
+pub type IoStream<T> = Box<dyn Stream<Item = T, Error = std_io::Error> + Send>;
 
 /// A convenience macro for working with `io::Result<T>` from the `Read` and
 /// `Write` traits.
@@ -65,6 +65,6 @@ pub use self::async_write::AsyncWrite;
 
 fn _assert_objects() {
     fn _assert<T>() {}
-    _assert::<Box<AsyncRead>>();
-    _assert::<Box<AsyncWrite>>();
+    _assert::<Box<dyn AsyncRead>>();
+    _assert::<Box<dyn AsyncWrite>>();
 }