Clean up some style (dart-lang/web_socket_channel#120)

Focus on the cross platform class in the README. From the issues we see
some folks aren't aware of the new `WebSocketChannel.connect`
constructor and get caught up with cross platform issues because they
originally picked single platform imports. The vast majority of use
cases are covered by the main import, so drop the sections on the
platform specific imports altogether.

Update some code samples in doc comments for style.

Remove some unnecessary library statements.
4 files changed
tree: c49c9137c1208f46c7cde67f8a83b2c7b10c36a2
  1. pkgs/