update changelog for 0.27 after merging new features

CHANGES.rst

@@ -2,16 +2,38 @@
 Cython Changelog
 ================
 
-
 0.27 (2017-??-??)
 =================
 
 Features added
 --------------
 
+* Extension module initialisation follows PEP 489 in CPython 3.5+, which resolves
+  several differences with regard to normal Python modules.  This makes the global
+  names ``__file__`` and ``__path__`` correctly available to module level code and
+  improves the support for module-level relative imports.
+  https://www.python.org/dev/peps/pep-0489/
+  (Github issues #1715, #1753)
+
+* Asynchronous generators (PEP 525) and asynchronous comprehensions (PEP 530)
+  have been implemented.  Note that async generators require finalisation support
+  in order to allow for asynchronous operations during cleanup, which is only
+  available in CPython 3.6+.  All other functionality has been backported as usual.
+  https://www.python.org/dev/peps/pep-0525/
+  https://www.python.org/dev/peps/pep-0530/
+
+* Annotations are now included in the signature docstring generated by the
+  ``embedsignature`` directive.  Patch by Lisandro Dalcin (Github issue #1781).
+
+* ``len(memoryview)`` can be used in nogil sections to get the size of the
+  first dimension of a memory view (``shape[0]``). (Github issue #1733)
+
 Bugs fixed
 ----------
 
+* Compile time ``DEF`` assignments were evaluated even when they occur inside of
+  falsy ``IF`` blocks. (Github issue #1796)
+
 
 
 0.26.1 (2017-??-??)