New Terminology section and illustrations.
Added multilayer example image.
Remove dependency on 'os/user', which cannot be used with CGO_ENABLED=0. This allows running the tests without CGO.
Merge pull request #932 from metalivedev/docs20130614

+ Documentation: Add terminology section
Merge pull request #990 from dotcloud/fix-tests-cgo

* Hack: remove dependency of unit tests on 'os/user', which cannot be used with CGO_ENABLED=0
Merge branch 'master' of git://github.com/dotcloud/docker into 111-bind-mounts