Item Amounts, New Config Messages

[meowsome]

Resolves #8

New additions:

• Add ability for user to specify item amount when giving item
• Add items one-by-one instead of all at once so that they fill up existing item stacks in the player's inventory and respect the item's max stack size
• Add tab completion for item amount as 3rd command argument
• Add reload and list commands to tab completion
• Add new config messages for item list, reload, player not found, item not found, and item limits

Things removed:

• Remove ability for username argument to be left blank when giving item because there'd be no way to get item amount

Changes:

• Changed config strings for full inventory, give item, receive item, and receive item when inventory full
• Changed help text for main command

Please let me know if I missed anything or if there's a better way of doing something.