It'd be nice if package:http exported HttpStatus constants

[jamesderlin]

trafficstars

The Dart SDK exports HttpStatus constants for both dart:io and dart:html. Actually using them in a platform-agnostic way is not particularly straightforward and is awkward.

Since one of the purposes of package:http is to provide a unified interface, it'd be nice if package:http exported them too.

[seifibrahim32]

@brianquinlan and this too please