Switch async code to use futures crate

[no111u3]

Remove using nb crate for asynchronously run code - use core::futures for replace it.
RFC for these changes is #172

[rust-highfive]

r? @thejpster

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[thejpster]

I like the idea, but it's a significant change so we should probably RFC it, or at least discuss it in the meeting.

We shall need to fix the build failures.

[thejpster]

Is there a reason this is using futures 0.1 instead of 0.3?

[no111u3]

@thejpster I fixed build on last commit. It is clean compatible changes with older code - only remove nb but need to switch minor version (I don't create RFC because it's may be applied anytime, It's try to make code clean). For reason of prefer 0.1 - it was my try to reproduce old PR #13, now I change it to core implementation without external crates. Thanks.

[korken89]

Interesting, I had no idea Poll had been stabilized.
We could probably replace the nb crate now.

[therealprof]

As per 11-26 meeting this will require an RFC to move ahead.

[Nemo157]

Moved to RFC

[no111u3]

@therealprof I added RFC on head message of this thread.

[no111u3]

@Nemo157 I understand that problem we have but in current implementation of api i couldn't change behavior of run without more breakable changes on api. I'm planning to find solution in this situation. Thanks.

[no111u3]

Need to review of architecture solution.