Made the optimizer_state serializable.

dlib/svm/svm_c_linear_dcd_trainer.h

@@ -327,6 +327,45 @@ namespace dlib
             std::vector<long> index;
             long dims;
             dlib::rand rnd;
+
+        public:
+            friend void serialize(const optimizer_state& item, std::ostream& out)
+            {
+                const int version = 1;
+                dlib::serialize(version, out);
+                dlib::serialize(item.did_init, out);
+                dlib::serialize(item.have_bias, out);
+                dlib::serialize(item.last_weight_1, out);
+                dlib::serialize(item.alpha, out);
+                dlib::serialize(item.w, out);
+                dlib::serialize(item.Q, out);
+                dlib::serialize(item.index, out);
+                dlib::serialize(item.dims, out);
+                dlib::serialize(item.rnd, out);
+            }
+
+            friend void deserialize(optimizer_state& item, std::istream& in)
+            {
+                int version = 0;
+                dlib::deserialize(version, in);
+                if (version != 1)
+                {
+                    throw dlib::serialization_error(
+                        "Error while deserializing dlib::svm_c_linear_dcd_trainer::optimizer_state, unexpected version."
+                        );
+                }
+
+                dlib::deserialize(item.did_init, in);
+                dlib::deserialize(item.have_bias, in);
+                dlib::deserialize(item.last_weight_1, in);
+                dlib::deserialize(item.alpha, in);
+                dlib::deserialize(item.w, in);
+                dlib::deserialize(item.Q, in);
+                dlib::deserialize(item.index, in);
+                dlib::deserialize(item.dims, in);
+                dlib::deserialize(item.rnd, in);
+            }
+
         };
 
         template <