COPYING: Fill in the <year> and <copyright holders> markers

COPYING: Fill in the <year> and <copyright holders> markers

This is a separate commit to make is extremely clear what parts of
this file I've written on my own, and which parts I copied from the
Open Source Initiative.  Probably overkill in this case, but sometimes
it's useful if your pulling someone else's work into your repository.

After editing COPYING in my text editor, I committed the changes with:

  $ git commit --all --verbose

We talked about the `--all` option in c481fb5 (README.md: Document the
syntax used in the README, 2013-11-29).  The `--verbose` option option
shows the diff in comments in your editor so you can check them while
you compose the commit message.  This is useful when you're explaining
complicated commits, and it also lets you verify that you are actually
committing what you think you're committing.