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.
fix regrettion in utils tests introduced by #980
Merge pull request #1003 from dotcloud/fix_utils_tests

fix regression in utils tests introduced by #980
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