Merge pull request #350 from ably/PUB-1828/tombstones-and-object-deletes

[PUB-1828] Add Objects spec for object and map entry tombstones, and OBJECT_DELETE message handling

Author: VeskeR

src/features.md

@@ -4821,6 +4821,8 @@ Presence ops.
     `OBJECT_SYNC`
   - `(OM2h)` `serial` string - an opaque string that uniquely identifies
     this object message
+  - `(OM2j)` `serialTimestamp` Time - a timestamp from the `serial`
+    field
   - `(OM2i)` `siteCode` string - an opaque string used as a key to
     update the map of `serial` values on an object
 - `(OM3)` The size of the `ObjectMessage` for [TO3l8](#TO3l8) is
@@ -4996,6 +4998,8 @@ Presence ops.
     been removed
   - `(OME2b)` `timeserial` string - the `serial`\#OM2h value of the last
     operation that was applied to the map entry
+  - `(OME2d)` `serialTimestamp` Time - a timestamp from the `timeserial`
+    field. It is only present if `tombstone` is `true`
   - `(OME2c)` `data` `ObjectData` object - the data that represents the
     value of the map entry.
 - `(OME3)` The size of the `ObjectsMapEntry` is calculated as follows:
@@ -5484,9 +5488,11 @@ Presence ops.
     server will send a `HEARTBEAT` or transport-level ping to the
     client. If the value is 0, the server will allow arbitrarily-long
     levels of inactivity.
-
-#### ChannelProperties
-
+  - `(CD2i)` `objectsGCGracePeriod` integer - the length of time, in
+    milliseconds, that the client library must wait before releasing
+    resources for tombstoned objects and map entries (see
+    [RTO10](../objects-features#RTO10))\
+    h4. ChannelProperties
 - `(CP1)` properties of a channel and its state
 - `(CP2)` The attributes of `ChannelProperties` consist of:
   - `(CP2a)` `attachSerial` string - contains the `channelSerial` that
@@ -6539,6 +6545,7 @@ wildcard to mean all clauses with a given prefix.
       maxMessageSize: Int // CD2c
       serverId: String // CD2g
       maxIdleInterval: Duration // CD2h
+      objectsGCGracePeriod: Int // CD2i
 
     class Message: // TM*
       constructor(name: String?, data: Data?) // TM4
@@ -6588,6 +6595,7 @@ wildcard to mean all clauses with a given prefix.
       operation: ObjectOperation? // OM2f
       object: ObjectState? // OM2g
       serial: String // OM2h
+      serialTimestamp: Time? // OM2j
       siteCode: String // OM2i
 
     class ObjectOperation // OOP*, internal
@@ -6626,6 +6634,7 @@ wildcard to mean all clauses with a given prefix.
     class ObjectsMapEntry // OME*, internal
       tombstone: Boolean? // OME2a
       timeserial: String? // OME2b
+      serialTimestamp: Time? // OME2d
       data: ObjectData? // OME2c
 
     class ObjectData // OD*, internal