create page and add notes about some API changes (ros2#94)

* create page and add notes about some API changes

* add link to D turtle release page placeholder

* move d turtle to future release section

Author: wjwwood

source/Releases.rst

@@ -33,6 +33,17 @@ A summary of releases of ROS 2 software is listed below.
    * - `alpha1-8 <Releases/Alpha-Overview>`
      - 31 August 2015 - 4 October 2016
 
+Upcoming releases:
+
+.. list-table::
+   :header-rows: 1
+
+   * - Future Release Overview
+     - Date
+   * - `Dashing Diademata <Releases/Release-Dashing-Diademata>`
+     - Summer 2019
+   
+
 For more details about each release, see the corresponding release overview.
 
 Release practices

source/Releases/Release-Dashing-Diademata

@@ -0,0 +1,39 @@
+
+ROS 2 Dashing Diademata (codename 'dashing'; Summer 2019)
+=========================================================
+
+.. contents:: Table of Contents
+   :depth: 2
+   :local:
+
+*Dashing Diademata* will be the fourth release of ROS 2.
+
+Supported Platforms
+-------------------
+
+To be determined.
+
+
+New features in this ROS 2 release
+----------------------------------
+
+To be determined.
+
+
+Changes since the Crystal release
+---------------------------------
+
+Changes since the `Crystal Clemmys <Release-Crystal-Clemmys>` release:
+
+* New API in `rmw`, a fini function for `rmw_context_t`:
+
+ * `rmw_context_fini <https://github.com/ros2/rmw/blob/c518842f6f82910482470b40c221c268d30691bd/rmw/include/rmw/init.h#L111-L136>`_
+ 
+* Modification of `rmw`, now passes `rmw_context_t` to `rmw_create_wait_set`:
+
+ * `rmw_create_wait_set <https://github.com/ros2/rmw/blob/c518842f6f82910482470b40c221c268d30691bd/rmw/include/rmw/rmw.h#L522-L543>`_
+
+Known Issues
+------------
+
+None yet.