docs: Updating changelog.rst to reflect updates in core

docs/changelog.rst

@@ -14,6 +14,22 @@ v0.15.0 (UNRELEASED)
 - Mopidy no longer supports Python 2.6. Currently, the only Python version
   supported by Mopidy is Python 2.7. (Fixes: :issue:`344`)
 
+**Core**
+- Tracklist has now the power to make decisions on which is the next/previous
+  song, along with previously playback associated features, such as randomness,
+  consumption, repeat and single. For that, a new method has been created to
+  mark songs, some Playback properties have been converted into functions and
+  both functions and properties have been moved into Tracklist to have more
+  modularity:
+      - Properties converted into functions that need arguments:
+        :meth:`get_tl_track_at_eot`, :meth:`get_tl_track_at_next`, 
+        :meth:`get_tl_track_at_previous` and :meth:`tracklist_position`
+      - Properties moved: :attr:`random`, :attr:`repeat`, :attr:`consume` and
+        :attr:`single`
+      - Method created: :meth:`mark`
+- Tracklist's get_tl_track_at_* and tracklist_position now need a tl_track as a
+  reference to give an answer.
+
 **Command line options**
 
 - Converted from the optparse to the argparse library for handling command line