Initial implementation of MarkerPage.
Use closures to count and mark.
Adjust callers to match.
Use base structs and embedding.
Move pagination to its own package.
Change identity endpoints and services.
Update acceptance tests.
Rename `LastMark` to `LastMarker`.
Rename "Self" to "Owner".
Turns out I can eliminate NewXyzPager funcs.
Adjust callers again.
Allow implementation code to specify headers.
Paginate the results of containers.List().
Update the acceptance tests to use pagination.
Paginate the objects.List call.
Adjust storage acceptance tests accordingly.
Merge pull request #203 from smashwilson/paginate-storage

Mark-and-limit pagination and storage