Added & implemented isUnarmed Method

The new `isUnarmed` method checks if the player is not holding a tool, as opposed to checking if the player is holding air. This means that attacking with something such as a dirt block would count as unarmed. This is used, rather than `whatever.getType() == Material.AIR`, to check if a player is unarmed.

Basically, this makes it easier for users to attack with unarmed when they have a full inventory. One shouldn't have to drop items if they have a full inventory to use unarmed moves.

Thanks for checking out the PR. I hope you all like/accept it!