GUI Improved: add sound prompt when task download finish, which can be configured in preferences dialog
GUI Improved: improve the context menu of floating window and system tray icon
GUI Improved: processing progress dialog will be displayed when add http task group
GUI Bugfix: fix the bug that the task start order is not correct if reduce task queue length while the queue is not empty
GUI Bugfix: fix the bug of version 0.81 that program can not run under win98/me
Core Improved: the NAT port mapping and Windows Firewall operation is moved to a separated toolkit program, therefor the CPU usage of main program decrease
Core Bugfix: fix the bug that the preview window will lose response if click stop button while preview video file of BT task
