[css-position] Update changes section

Author: fantasai

css-position/Overview.bs

@@ -2317,19 +2317,15 @@ Acknowledgments</h2>
 
 <h2 class="no-num" id="changes">Changes</h2>
 
-<h3 id="changes-201207">
-Changes since the 7 February 2012 WD</h3>
+<h3 id="changes-201502">
+Changes since the 3 February 2015 WD</h3>
 
   The following significant changes were made since the
-  <a href="https://www.w3.org/TR/2012/WD-css3-positioning-20120207/">7 February 2012 Working Draft</a>
+  <a href="https://www.w3.org/TR/2015/WD-css3-positioning-20150203/">5 February 2015 Working Draft</a>
 
   <ul>
-    <li>Added Rossen Atanassov as a new editor
-    <li>Added ''sticky'' keyword to the 'position' property to define the sticky
-      positioning behavior.
-    <li>Added logical offset keywords 'offset-before', 'offset-end', 'offset-after'
-      and 'offset-start'
-    <li>Added new attachment properties 'attachment-type', 'attachment-top', 'attachment-right',
-      'attachment-bottom', 'attachment-left', 'attachment'
-    <li>Removed 'clip' property section.
+    <li>Added informative table to clarify positioning calculations.
+    <li>Removed “page” and “center” positioning schemes,
+    which had not in fact been approved by the CSSWG
+    and should not have been published in the first place.
   </ul>