Docs: package overview shows list of dates

Before
--------
Every package file starts with:

  // some date
  package ui

and this is picked up by godoc.

After
------
Modified files with an empty comment and added a proper comment in init.go:

// ui is a simple library for building cross-platform GUI programs in Go.
//
// It targets Windows, Mac OS X, Linux, and other Unixes, and provides a
// thread-safe, channel-based API.
package ui


All files have also been formatted with go fmt (version 1.2.1).
Thank you,

  Tom