Add a new function to create an `ArrayVar` from a slice. Change `ArrayVar`s mutating function to take &mut self.
Add a new function to create an `ArrayVar` from a slice. Change `ArrayVar`s mutating function to take &mut self.

DiamondLovesYou/rust-ppapi,DiamondLovesYou/rust-ppapi,DiamondLovesYou/rust-ppapi,DiamondLovesYou/rust-ppapi