Add new plots and items

[b]Update[/b] [img]{STEAM_CLAN_IMAGE}/42161504/303f9e736db927f1085dff0a6c5d2db4855f3b0a.png[/img] 1. Add a new plot. [img]{STEAM_CLAN_IMAGE}/42161504/8141f81386a14f2379c1ef8a0c5816ba44363a8b.png[/img] 2. Add new item Xuanyuan Sword. 3. Fix the treasure chest drop bug. 4. Fix cave movement bug. 5. Fix boss movement bug. [b]Next step[/b] 1. Add more new plots. 2. Prepare to start a new chapter. 3. Add new mission item.