Async read callback doesn't support user argument

[jdavidberger]

Currently the read callback doesn't support a user argument, which severely limits it's usefulness. Is there a fundamental reason this isn't possible?

If it's helpful I can submit a PR with that change. I'd also like to see async versions of the write calls and could include those too.

[oliviermartin]

HI @jdavidberger, as far as I remember there is no valid reason these functions do not support user argument. Feel free to create a PR and I will be happy to review/merge it.