- Formally defined how array2d objects must lay their components out in memory

- Added width_step() to array2d to help define the memory layout.  Also added
   it to cv_image to keep the interfaces compatible.
 - Fixed a typo in the deserialize for array2d objects.  The template wasn't
   declared properly.

dlib/array2d/array2d_kernel_1.h

@@ -284,6 +284,12 @@ namespace dlib
         unsigned long size (
         ) const { return static_cast<unsigned long>(nc_ * nr_); }
 
+        long width_step (
+        ) const
+        {
+            return nc_;
+        }
+
     private:
 
         // this object exists just so we can have a row type object that
@@ -348,10 +354,11 @@ namespace dlib
     }
 
     template <
-        typename T 
+        typename T,
+        typename mem_manager
         >
     void deserialize (
-        array2d<T>& item, 
+        array2d<T,mem_manager>& item, 
         std::istream& in
     )   
     {

dlib/array2d/array2d_kernel_abstract.h

@@ -50,6 +50,12 @@ namespace dlib
 
                 Also note that unless specified otherwise, no member functions
                 of this object throw exceptions.
+
+
+                Finally, note that this object stores each row of data contiguously 
+                in memory, and the overall layout is in row major order.  However,
+                there might be padding at the end of each row.  To determine the
+                offset from one row to another you can use step_width(). 
         !*/
 
 
@@ -199,6 +205,14 @@ namespace dlib
                 - swaps *this and item
         !*/ 
 
+        long width_step (
+        ) const;
+        /*!
+            ensures
+                - returns the pointer offset to step from one row to another.
+                  That is, &item[0][0] + step_width(item) == &item[1][0].
+        !*/
+
     private:
 
         // restricted functions

dlib/opencv/cv_image.h

@@ -61,6 +61,7 @@ namespace dlib
 
         long nr() const { return _nr; }
         long nc() const { return _nc; }
+        long width_step() const { return _widthStep; }
 
         cv_image& operator=( const cv_image& item)
         {

dlib/opencv/cv_image_abstract.h

@@ -142,6 +142,13 @@ namespace dlib
                 - returns #*this
         !*/
 
+        long width_step (
+        ) const;
+        /*!
+            ensures
+                - returns the pointer offset to step from one row to another.
+                  That is, &item[0][0] + step_width(item) == &item[1][0].
+        !*/
     };