Sort changelog entry files by file name

This stabilizes the changelog order, preventing non-deterministic
website builds, and also allows ordering the entries manually by
naming the files according to the desired lexicographical order.

changed.d

@@ -232,6 +232,7 @@ auto readTextChanges(string changelogDir)
 
     return dirEntries(changelogDir, SpanMode.shallow)
             .filter!(a => a.name().endsWith(".dd"))
+            .array.sort()
             .map!readChangelog
             .filter!(a => a.title.length > 0);
 }