Add plugin spec for Objects

Also renames feature spec for `Objects` to `RealtimeObjects`.
In the future we may add the REST API support for Objects, and it is
only reasonable to name that `RestObjects`. To stay consistent with the
namings for other features (e.g. RestChannels - RealtimeChannels) we
should rename the spec for `Objects` to `RealtimeObjects`

Author: VeskeR

textile/features.textile

@@ -23,6 +23,7 @@ jump_to:
     - Channels#realtime-channels
     - RealtimeChannel#realtime-channel
     - RealtimePresence#realtime-presence
+    - RealtimeObjects#realtime-objects
     - EventEmitter#eventemitter
     - Forwards compatibility#realtime-compatibility
     - State conditions and operations#state-conditions-and-operations
@@ -385,13 +386,15 @@ h3(#plugins). Plugins
 * @(PC2)@ No generic plugin interface is specified, and therefore there is no common API exposed by all plugins. However, for type-safety, the opaque interface @Plugin@ should be used in strongly-typed languages as the type of the @ClientOptions.plugins@ collection as per "TO3o":#TO3o.
 * @(PC3)@ A plugin provided with the @PluginType@ enum key value of @vcdiff@ should be capable of decoding "vcdiff"-encoded messages. It must implement the @VCDiffDecoder@ interface and the client library must be able to use it by casting it to this interface.
 ** @(PC3a)@ The base argument of the @VCDiffDecoder.decode@ method should receive the stored base payload of the last message on a channel as specified by "RTL19":#RTL19. If the base payload is a string it should be encoded to binary using UTF-8 before being passed as base argument of the @VCDiffDecoder.decode@ method.
+* @(PC5)@ A plugin provided with the @PluginType@ enum key value of @Objects@ should provide the "RealtimeObjects":#RTO1 feature functionality for realtime channels ("RTL27":#RTL27). The plugin object itself is not expected to provide a public API. The type of the plugin object, and how it enables the Objects feature for a realtime channel, are left for individual implementations to decide.
 * @(PC4)@ A client library is allowed to accept plugins other than those specified in this specification, through the use of additional @ClientOptions.plugins@ keys defined by that library. The library is responsible for defining the interface of these plugins, and for making sure that these keys do not clash with the keys defined in this specification.
 
 h3(#plugin-type). PluginType
 
 * @(PT1)@ @PluginType@ is an enum describing the different types of plugins that the library supports. See the @ClientOptions#plugins@ property ("TO3o":#TO3o).
 * @(PT2)@ @PluginType@ takes one of the following values:
 ** @(PT2a)@ @vcdiff@ – see "PC3":#PC3.
+** @(PT2b)@ @Objects@ – see "PC5":#PC5.
 
 h3(#vcdiff-decoder). VCDiffDecoder
 
@@ -775,6 +778,9 @@ h3(#realtime-channel). RealtimeChannel
 ** @(RTL8b)@ Unsubscribe with a name argument and a listener argument unsubscribes the provided listener if previously subscribed with a name-specific subscription
 * @(RTL9)@ @RealtimeChannel#presence@ attribute:
 ** @(RTL9a)@ Returns the @RealtimePresence@ object for this channel
+* @(RTL27)@ @RealtimeChannel#objects@ attribute:
+** @(RTL27a)@ Returns the @RealtimeObjects@ object for this channel "RTO1":#RTO1
+** @(RTL27b)@ It is a programmer error to access this property without first providing the @Objects@ plugin ("PC5":#PC5) in the client options. This programmer error should be handled in an idiomatic fashion; if this means accessing the property should throw an error, then the error should be an @ErrorInfo@ with @statusCode@ 400 and @code@ 40019.
 * @(RTL10)@ @RealtimeChannel#history@ function:
 ** @(RTL10a)@ Supports all the same params as @RestChannel#history@
 ** @(RTL10b)@ Additionally supports the param @untilAttach@, which if true, will only retrieve messages prior to the moment that the channel was attached or emitted an @UPDATE@ indicating loss of continuity. This bound is specified by passing the querystring param @fromSerial@ with the @RealtimeChannel#properties.attachSerial@ assigned to the channel in the @ATTACHED@ @ProtocolMessage@ (see "RTL15a":#RTL15a). If the @untilAttach@ param is specified when the channel is not attached, it results in an error
@@ -930,9 +936,9 @@ then the @enter@ request results in an error immediately.
 ** @(RTP15e)@ Implicitly attaches the @RealtimeChannel@ if the channel is in the @INITIALIZED@ state. However, if the channel is in or enters the @DETACHED@ or @FAILED@ state before the operation succeeds, it will result in an error
 ** @(RTP15f)@ If the client is identified and has a valid @clientId@, and the @clientId@ argument does not match the client's @clientId@, then it should indicate an error. The connection and channel remain available for further operations
 
-h3(#objects). Objects
+h3(#realtime-objects). RealtimeObjects
 
-Reserved for @Objects@ feature specification. Reserved spec points: @OBJ@, @LM@, @LC@
+Reserved for @RealtimeObjects@ feature specification. Reserved spec points: @RTO@, @RTLO@, @RTLC@, @RTLM@
 
 h3(#realtime-annotations). RealtimeAnnotations
 
@@ -2314,6 +2320,7 @@ class RealtimeChannel: // RTL*
   state: ChannelState // RTL2b
   whenState(ChannelState, (ChannelStateChange?) ->) // RTL25
   presence: RealtimePresence // RTL9
+  objects: RealtimeObjects // RTL27
   properties: ChannelProperties // RTL15
   // Only on platforms that support receiving push notifications:
   push: PushChannel // RSH7
@@ -2853,6 +2860,7 @@ class Plugin // PC2
 
 enum PluginType // PT*
   "vcdiff" // PT2a
+  "Objects" // PT2b
 
 class VCDiffDecoder // VD*
   decode([byte] delta, [byte] base) -> [byte] // VD2a, PC3a