Rename EventQueue to Channel

[dherman]

This PR experiments with renaming the event queue API:

• neon::event::EventQueue -> neon::event::Channel
• neon::event::EventQueueError -> neon::event::SendError

This is based on an insight @kjvalencik made recently: a clone/copy/sync-able data structure that gives access across multiple threads to the Node.js runtime's internal event queue by a send operation that communicates across threads is much closer conceptually to Rust's idiomatic concept of channels than it is to being an abstraction of the JS event queue itself.

The PR attempts to make the change conservatively, preserving the previous names as aliases for the new names but adding deprecation attributes and hiding them from API docs. This allows us to ship the new name without breaking existing customers and eventually remove the deprecated names in a future release.

Here's a preview of updated neon::event docs with code examples where you can see how the code looks with the renamed API.

[kjvalencik]

I really, really like this naming change. I think it clarifies a lot. It also resolves some naming questions for when we implement bounded queues. We can call it cx.sync_channel().

[dherman]

I really, really like this naming change. I think it clarifies a lot.

Right?? I'm so glad you brought this idea up.

It also resolves some naming questions for when we implement bounded queues. We can call it cx.sync_channel().

Oh, I like that. I know it's FCP, but we should probably update neon-bindings/rfcs#32 with the new name and a note about sync_channel() listed as a possible future extension.

[dherman]

@kjvalencik Do you think this is ready to merge?