New crate: Provide iterator-like methods on a crossbeam channel

[JackKelly]

Whilst writing a code sketch for decompressing data, it occurred to me that it'd be nice to have a crate which:

• wraps a crossbeam channel
• provides iterator-like methods on those buffers (map, etc.)
• defines a struct to wrap buffers with some metadata (see How to identify each returned Item? #105)

Related

• Use a flat crate structure so this git repo can store multiple (interconnected) crates in a single workspace #94
• New crate: apply a user-supplied function to a Stream of buffers #26

[JackKelly]

Wait, maybe this isn't necessary!? We can already iterate over channels! And we can use Rayon::par_iter to iterate in parallel! So maybe we just need some functions (to pass to par_iter().map()) which respect each item's metadata?

[JackKelly]

Sorry, I'm an idiot, this is totally unnecessary... we can just use par_iter! Here's a quick code sketch.