message: bookmark changelog
diff: * `Reflector` now has basic signal handling #152
  * `Api::watch` no longer filters out error events (`next` -> `try_next`)
  * `Api::watch` returns `Result<WatchEvent>` rather than `WatchEvent`
  + * `WatchEvent::Bookmark` added to enum
  + * `ListParams::allow_bookmarks` added
  0.31.0 / 2020-03-27
  ===================
  