Initial implementation returning series of oneshot::Receiver instead …

[jeikabu]

…of single Stream (mpsc::Receiver)

AsyncStream provides create_async_stream which are used as stream of NngMsg (futures::Stream)

Explicitly use oneshot/mpsc namespace so it's clearer what's going on

Pair with read async context where receive returns a oneshot::Receiver

Rename async-related structs/traits

• create_async_context() => create_async()
• AsyncContext => AsyncHandle (to avoid confusion between "context" and nng_ctx)

Unify naming and implementation of pair, pull, and sub

Add non-Stream version of async replier (using oneshot channel)

Move async protocols to asyncio/

cargo fix and fmt