Modernize the package's style.

README.md

-# Async utilities package
-
-Contains tools to work with asynchronous computations.
-
-The package contains `Stream` and `Future` related functionality,
-as well as sub-libraries with different utilities.
+Contains utility classes in the style of `dart:async` to work with asynchronous
+computations.
 
 ### Zipping streams
 
-The "stream_zip.dart" sub-library contains functionality
-to combine several streams of events into a single stream of tuples of events.
+The `StreamZip` class can combine several streams of events into a single stream
+of tuples of events.
 
 ### Results
-The "result.dart" sub-library introduces a `Result` class that can hold either
-a value or an error.
-It allows capturing an asynchronous computation which can give either a value
-or an error, into an asynchronous computation that always gives a `Result`
-value, where errors can be treated as data.
-It also allows releasing the `Result` back into an asynchronous computation.
 
-### History.
-This package is unrelated to the discontinued `async` package with version 0.1.7.
-
-## Features and bugs
-
-Please file feature requests and bugs at the [issue tracker][tracker].
-
-[tracker]: https://github.com/dart-lang/async/issues
+The package introduces a `Result` class that can hold either a value or an
+error. It allows capturing an asynchronous computation which can give either a
+value or an error, into an asynchronous computation that always gives a `Result`
+value, where errors can be treated as data. It also allows releasing the
+`Result` back into an asynchronous computation.