Migration guide from 0.1 to 0.3

[nicholasbishop]

I've been trying to update some code written with futures 0.1 to use futures 0.3, but I've found that the API has changed so much that I just don't know how to proceed in some cases. I did find this helpful blog post: https://www.ncameron.org/blog/migrating-a-crate-from-futures-0-1-to-0-3, but that's about it. I think a migration guide would be really nice, and could help with more quickly moving the ecosystem from 0.1 to 0.3.

A migration document could contain the following sections:

• A list of simple renames, e.g. try_ready -> ready.
• How to update implementations of traits that have evolved, e.g. Future and Sink. (As that blog post notes, Sink in particular is not so easy to migrate.)
• What to do for APIs that no longer exist, e.g. the Notify trait.

[yoshuawuyts]

https://github.com/rust-lang/async-book seems like a good place for this to go. I suspect that unless someone takes the lead on authoring this document it won't happen though; @nicholasbishop would this be something you'd like to do?