Refactor the annotation tests to share setup.
Add json output for the Annotation class.
Globalize the example manifest location for all tests.
Return "/" by default for Manifest#id.
Refactor Manifest for easier serialization.

The internal structure is now kept intact, ready for conversion to JSON.
Improve Util#clean_json.

Now cleans out all things that can be detected as empty.
Add Manifest#to_json.
Add write support for Manifest#id.
Write support for Manifest#created_on and #authored_on.