Small changes to cheat_core_items.lua

[wilecoyote]

• Corrected the descriptions for cheat_add_item The description for health was wrong. Using the command cheat_add_item id:ui_nm_arrow_hunter amount:10 health:50 doesn't work. It must be: cheat_add_item id:ui_nm_arrow_hunter amount:10 health:0.5
• Limited cheat_damage_all_items to ammo, armor and weapons. I think only items stated in the description should be damaged.