Make this library async-friendly

[ntninja]

Currently all of this library assumes synchronous I/O, considering that that is bad practice when interacting with the network datastore implementations and doesn't align with our goals for py-ipfs. Using anyio for this would likely be “good enough” and not require us to bind ourselves to one specific event loop while the asyncio vs trio debate is still ongoing.

[ntninja]

Looks like anyio currently does not provide support for any kind of asynchronous I/O streams. Without those, using it will become quite verbose and add lots of boilerplate code.

After contemplating, I think going with trio for now should be OK. Once we have a working setup with one AIO library, translating the code to another shouldn't be too much work.

@AliabbasMerchant: Any opinions on this?

[AliabbasMerchant]

@Alexander255 To be honest, I've never properly worked with any Async I/O library in Python. So no idea. Let me check out a few of the libraries.

[ntninja]

Bump. I've now converted the entire py-datastore core to async using trio, so far our dependence on trio is rather weak and changing the asyncio framework would mostly consist of renaming a few methods and changing some imports. But the more I convert the harder it will likely get, so it would be useful to have a decision very soon.

[AliabbasMerchant]

Lets go with trio

[AliabbasMerchant]

@Alexander255 Umm... (Did you forget to create a PR? Or is it still WIP?)

[ntninja]

Ok thanks! I must admit that my codebase right now has not only the async/await port, but also the complete ObjectDatastore/BinaryDatastore split – so it's gonna be quite a large PR, I fear.

I couldn't complete it yesterday though, as I got carried away adding typing annotations to some stuff that apparently cannot be represented by mypy at this time. (It was useful for finding a bunch of other inconsistencies before this however, so adding annotations wasn't just a waste of time like in this latest case involving cooperative multiple inheritance.)

I'll try to open a PR today though.

[AliabbasMerchant]

Type annotations are awesome!

[ntninja]

See #12

[adamjsawicki]

@Alexander255 can this be closed because of #12?

[ntninja]

@swixx: Yes, although the FS datastore provider hasn't been updated yet in master (see #13).

@AliabbasMerchant @seenivasanseeni: May I have a review on #13 please? 🙂