Issue #4580: slicing of memoryviews when itemsize != 1 is wrong.
Also fix len() to return number of items rather than length in bytes.

I'm sorry it was not possible for me to work on this without reindenting
a bit some stuff around. The indentation in memoryobject.c is a mess,
I'll open a separate bug for it.
diff --git a/Misc/NEWS b/Misc/NEWS
index 7b3a291..c3d7074 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,10 @@
 Core and Builtins
 -----------------
 
+- Issue #4580: Fix slicing of memoryviews when the item size is greater than
+  one byte. Also fixes the meaning of len() so that it returns the number of
+  items, rather than the size in bytes.
+
 - Issue #4075: Use OutputDebugStringW in Py_FatalError.
 
 - Issue #4747: When the terminal does not use utf-8, executing a script with