Update `CHANGELOG.md`

* Include missing references.
* Improve consistency.
* Wrap text at 80 characters.
Remove default margin from print styles

Providing a default value (such as `5cm`) for the print margins is
problematic because:

 1) in some browsers, it prevents users from customizing the browser
    print settings
 2) in some contexts (browser/os/printer), the value may be too:
    * small, and the margins may collide with all the different
      headers/footers (URL, date, etc) that are usually printed
      by default
    * big, and the margins will just waste the space

Most browsers provide a default non-zero value for the print margins,
so it's better to not specify a value at all, and just let them handle
this themselves.

See also:

 * http://www.w3.org/TR/css3-page/#at-page-rule
 * https://developer.mozilla.org/en-US/docs/Web/CSS/@page

Close #1477.