[C++] API sync

Added:

  * NCKey: `ScrollUp`, `ScrollDown` and `Return`
  * Plane: is_mouse_event (`ncplane_mouseevent_p`)

include/ncpp/NCKey.hh

@@ -109,6 +109,9 @@ namespace ncpp
 		static constexpr char32_t Button10  = NCKEY_BUTTON10;
 		static constexpr char32_t Button11  = NCKEY_BUTTON11;
 		static constexpr char32_t Release   = NCKEY_RELEASE;
+		static constexpr char32_t ScrollUp  = NCKEY_SCROLL_UP;
+		static constexpr char32_t ScrollDown = NCKEY_SCROLL_DOWN;
+		static constexpr char32_t Return    = NCKEY_RETURN;
 
 		static bool IsMouse (char32_t ch) noexcept
 		{

include/ncpp/Plane.hh

@@ -882,6 +882,11 @@ namespace ncpp
 			return cell.has_no_foreground ();
 		}
 
+		bool is_mouse_event (const ncinput *ni) const noexcept
+		{
+			return ncplane_mouseevent_p (plane, ni);
+		}
+
 		const char* get_extended_gcluster (Cell &cell) const noexcept
 		{
 			return cell_extended_gcluster (plane, cell);