Added spec for the csv matrix output method.

dlib/matrix/matrix_abstract.h

@@ -733,6 +733,14 @@ namespace dlib
               from being parsed into a matrix then #in.fail() == true.
     !*/
 
+    some_undefined_iomnaip_type csv;
+    /*!A csv
+        This object is used to define an io manipulator for matrix expressions.  In
+        particular, you can write statements like:
+            cout << csv << yourmatrix;
+        and have it print the matrix with commas separating each element.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <typename EXP>