Remove copyright element from Mallard

[Shaun McCance <shaunm gnome org>]

http://www.gnome.org/~shaunm/mallard/mal_info_copyright.html
http://www.gnome.org/~shaunm/mallard/mal_info_credit.html

Working with the some Mallard documents, I can't help
but be annoyed by the redundancy between credits and
copyright information.  I'm proposing we get rid of
the copyright element and let credit optionally have
a year (or years) element as a child.

So instead of this:

  <credit type="author">
    <name>Shaun McCance</name>
    <email>shaunm gnome org</email>
  </credit>
  <copyright>
    <year>2009</year>
    <name>Shaun McCance</name>
    <email>shaunm gnome org</email>
  </copyright>

We'd just write this:

  <credit type="author">
    <year>2009</year>
    <name>Shaun McCance</name>
    <email>shaunm gnome org</email>
  </credit>

Credits that don't get copyright (e.g. reviewers) don't
have to have the year element.  And copyright holders
that aren't otherwise contributors (e.g. entities we
assign copyright to) can just omit the type attribute.
Or maybe type can be "copyright".

Thoughts?

--
Shaun