Documentation: update URLs for Richard Gooch's articles

Current URL for "Kernel API changes from 2.0 to 2.2" hasn't been available
for some time, updating. The second article about changes from 2.2 to 2.4
is missing a URL, adding it.

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>