Make T: Copy for &[T] streams

[Marwes]

As was pointed out to me by @m4rw3r &[T] streams are usually on &[u8] or other types T which are copyable. This would allow the Item type of such streams to be T rather than &T but has the downside that you can use &[T] where T != Copy. A newtype could be added which wraps such &[T] slices allowing for &T items again.

Alternatives:

• Introduce a newtype which can be used to wrap slices with T: Copy instead.

#[derive(Debug, PartialEq, Clone)]
struct CopySlice<'a, T: 'a>(&'a [T]);

impl <'a, T: Positioner + Copy + 'a> Stream for CopySlice<'a, T> {
    type Item = T;
    type Range = &'a [T];
    fn uncons(self) -> Result<(T, CopySlice<'a, T>), Error<T, CopySlice<'a, T>> {
        ...
    }
}

I don't have much of any opinion either way but it needs to be decided before 1.0. Wrapping the slice in a newtype is only necessary for the first call to parse so its only a minor ergonomic win for the case which does not need wrapping, it's more of deciding which way is the least surprising for the majority of users.

[Marwes]

Given how much a usability boost this gives for &[u8] which I would expect is the most common slice to parse I am going to merge this. For non copy-able slices just wrap the input slice with the added SliceStream type.