doc: add skeletons for *_with_timestamp_column (googleapis/google-cloud-cpp-spanner#1220)
doc: add skeletons for *_with_timestamp_column (googleapis/google-cloud-cpp-spanner#1220)

* doc: add skeletons for *_with_timestamp_column

This should unblock our doc writer.

Part of googleapis/google-cloud-cpp-spanner#1217, googleapis/google-cloud-cpp-spanner#1218, googleapis/google-cloud-cpp-spanner#1219

* tidy fixes

* tidy fixes take 2

googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp