Context: add a numeric_param property

src/context.hh

@@ -42,10 +42,15 @@ struct Context
         return GlobalOptionManager::instance();
     }
 
+    int numeric_param() const { return m_numeric_param; }
+    void numeric_param(int param) { m_numeric_param = param; }
+
+
 public:
     safe_ptr<Window> m_window;
     safe_ptr<Buffer> m_buffer;
 
+    int m_numeric_param = 0;
 };
 
 }