Added operator= that takes an initializer_list so that = assignments always

behave in the way you would expect.

dlib/matrix/matrix.h

@@ -1163,6 +1163,12 @@ namespace dlib
 
         }
 
+        matrix& operator=(const std::initializer_list<T>& l)
+        {
+            matrix temp(l);
+            temp.swap(*this);
+            return *this;
+        }
 
         matrix(matrix&& item)
         {

dlib/matrix/matrix_abstract.h

@@ -494,6 +494,19 @@ namespace dlib
                 - returns *this
         !*/
 
+        matrix& operator=(
+            const std::initializer_list<T>& l
+        );
+        /*!
+            requires
+                - This matrix is capable of having a size() == l.size().  Therefore, if
+                  NR*NC != 0 then l.size() must equal NR*NC.  Alternatively, if NR or NC is
+                  != 0 then l.size() must be a multiple of the non-zero NR or NC.
+            ensures
+                - Assigns the contents of l to *this by performing: matrix(l).swap(*this)
+                - returns *this
+        !*/
+
         template <typename EXP>
         matrix& operator= (
             const matrix_exp<EXP>& m