doc: Remove old issues and add a note about CreateMode (the LOCAL/REPLICATED thing)

doc/c++_notes.txt

@@ -0,0 +1,9 @@
+Buildat C++ Notes
+=================
+
+Urho3D: Scene replication
+-------------------------
+Make sure to explicitly pass LOCAL or REPLICATED as the CreateMode for
+Node::CreateChild() and Node::CreateComponent(); otherwise you WILL cause
+unexpected issues at a very unexpected point of time.
+

doc/external_issues.txt

@@ -1,10 +1,3 @@
 Issues in other projects affecting Buildat
 ==========================================
 
-Urho3D:
-- It is not possible to implement any kind of custom loading functionality into
-  Urho3D::ResourceCache. It is not inheritable, and it does not provide any way
-  to insert custom loaders in other ways. The only thing we can currently do is
-  wrap GetResource in Lua, and copy the files into a temporary file structure
-  before calling the actual GetResource.
-

doc/todo.txt

@@ -65,4 +65,3 @@ Buildat TODO
 - Debug instability in server at module reload
 - An option in the server to just compile and quit (to be used when one wants to
   check for compiler errors but not actually run anything)
-- Figure out why digger doesn't work properly when the client connects via menu