v10.0.0

• Breaking: onDelivered replaces onDeliveryReceiptReceived. The
  hook gets one DeliveredEvent for each new receipt source of each
  recipient device. A Relay receipt gives source: 'relay' and
  decryptionConfirmed: false. An end-to-end receipt gives
  source: 'e2ee' and decryptionConfirmed: true. The status of a device
  only moves forward, sources holds each source that the device has given
  so far, and a second receipt of the same source changes nothing. A receipt
  for a send that has not resolved yet comes after the send resolves. The
  new DeliveredEvent and DeliverySource types are exported.
• Breaking: an unknown hook name throws. registerHook() and the
  hooks option of client creation throw for a name that is not a hook.
• Breaking: the server_delivery_receipt message type and
  IMPLICIT_ENVELOPE_TYPES are removed. An envelope is implicit only
  when its contentHint is ContentHint.Implicit.
• Changed: only an end-to-end receipt deletes the retry copy. The
  sender deletes its copy of a message for a recipient device when that
  device sends an end-to-end delivery receipt. A Relay receipt does not
  delete it.
• Changed: end-to-end receipts are sealed when the client can seal
  them. The client seals a delivery receipt when it holds the access key
  of the sender, and sends it identified otherwise. A receipt follows the
  sealed sender delivery mode of a message: in 'required' mode the client
  does not send a receipt that it cannot seal, and a Relay that refuses the
  access key does not make the receipt identified.
  sendMultiRecipientUnidentified() takes an optional contentKind, so a
  sealed receipt carries 'receipt'.
• Added: each envelope names its content kind. Envelope has an
  optional contentKind, of the new exported ContentKind type. The client
  sets 'receipt' on each end-to-end delivery, read, and viewed receipt
  that it sends. The Signal Protocol Relay transport sends 'message' for every
  other envelope, on identified, anonymous and group sends, so the Relay
  can tell a receipt from a message without reading it.
• Added: the client takes Relay delivery receipts from the Signal
  Protocol Relay. A Relay that states the receipt capability on a
  connection sends delivery-receipt frames on that connection, and a pull
  returns its receipts only when it asks for them. The client passes each
  receipt through the same ordered queue as the messages, hands each receipt
  ID off once, and acknowledges it to the Relay after the hand-off, in
  frames of at most 100 IDs on the socket or with receiptIds over HTTP.
  A Relay receipt states only that the recipient device acknowledged the
  message to the Relay, not that the device decrypted it.
• Changed: deliveryReceipts: 'auto' leaves the receipt to the Relay
  when it can. On the Signal Protocol Relay, the client sends no
  end-to-end delivery receipt for an identified message that the Relay
  acknowledgment lists as receipted. It sends the end-to-end receipt when
  the acknowledgment omits the message, when it fails, when no reply comes
  in 30 seconds, or when the connection closes first. A sealed message
  always gets the end-to-end receipt. stop() sends each receipt that
  still waits for a Relay reply, once. On any other relay, 'auto' sends
  the same receipts as 'always'.