Merge pull request #3608 from Unity-Technologies/develop-sidechannel-changelog

update changelog and migration guide for sidechannel changes

com.unity.ml-agents/CHANGELOG.md

  - The `IFloatProperties` interface has been removed.
  - Fix #3579.
  - Fixed an issue when using GAIL with less than `batch_size` number of demonstrations. (#3591)
+ - The interfaces to the `SideChannel` classes (on C# and python) have changed to use new  `IncomingMessage` and `OutgoingMessage` classes. These should make reading and writing data to the channel easier. (#3596)
 
 ## [0.14.1-preview] - 2020-02-25
 

docs/Migrating.md

   * `Done()` was renamed to `EndEpisode()`
   * `GiveModel()` was renamed to `SetModel()`
 * The `IFloatProperties` interface has been removed.
+* The interface for SideChannels was changed:
+  * In C#, `OnMessageReceived` now takes a `IncomingMessage` argument, and `QueueMessageToSend` takes an `OutgoingMessage` argument.
+  * In python, `on_message_received` now takes a `IncomingMessage` argument, and `queue_message_to_send` takes an `OutgoingMessage` argument.
 
 ### Steps to Migrate
 * Add the `using MLAgents.Sensors;` in addition to `using MLAgents;` on top of your Agent's script.
   * `Done()` to `EndEpisode()`
   * `GiveModel()` to `SetModel()`
 * Replace `IFloatProperties` variables with `FloatPropertiesChannel` variables.
+* If you implemented custom `SideChannels`, update the signatures of your methods, and add your data to the `OutgoingMessage` or read it from the `IncomingMessage`.
 
 ## Migrating from 0.13 to 0.14