get_bytes for Buf trait

[Diggsey]

fn get_bytes(&mut self, size: usize) -> Bytes

This is somewhat similar to #228 but for reading from a Buf.

The idea is that a Buf implementation may already have an efficient way to get a "view" of some of its bytes that does not involve an expensive copy. The default implementation would just allocate a new Bytes object and then use copy_to_slice.

The Bytes type could have a specialized implementation that just calls split_to on itself. In the future it may be possible to specialize the implementation of Buf for &'static [u8] too, since Bytes can cope with that, or maybe Bytes will get an optional lifetime parameter allowing it to hold reference of any lifetime.

[danburkert]

I think this is fixed by #439.

[Diggsey]

Yep 👍