Add EventRedact() prototype.

TODO.txt

@@ -22,7 +22,7 @@ Milestone: v0.4.0
         [x] Rename Sha2.h to just Sha; add Sha1() function
         [x] Make Sha256() return raw bytes; add function to
             convert to hex string.
-    [ ] 8: Rooms
+    [~] 8: Rooms
     [~] 9: User Data
         [x] Profiles
         [~] Directory

src/include/Event.h

@@ -52,4 +52,10 @@ extern char * EventContentHash(HashMap *);
  */
 extern char * EventIdGet(Room *, HashMap *);
 
+/**
+ * Redact an event according to the rules for the given
+ * room. The event is modified in place.
+ */
+extern int EventRedact(Room *, HashMap *);
+
 #endif /* TELODENDRIA_EVENT_H */