Bump tokio from 0.2.11 to 0.3

[Urhengulas]

This PR shall update tokio to version 0.3.

Changes

• adapt AsyncRead, AsyncWrite implementations
• rename delay_for -> sleep, Delay -> Sleep
• ...

Fixes #2302

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There are still quite some errors left to resolve, so I am happy to get some input there 😃

[paolobarbolini]

This should fix it

Suggested change

	// TODO: There should be a way to do following two lines cleaner...
	buf.put_slice(prefix.to_vec().as_slice());
	buf.put_slice(&prefix[..copy_len]);

[seanmonstar]

Thanks for this! I had also started a branch just yesterday doing this, which was useful to find all the things that aren't easily fixable in hyper, and started trying to put them back into Tokio. The biggest one is vectored writes, but there's a few smaller things too. I'll list them in the original issue.

[Urhengulas]

@seanmonstar: Thanks for this! I had also started a branch just yesterday doing this, which was useful to find all the things that aren't easily fixable in hyper, and started trying to put them back into Tokio. The biggest one is vectored writes, but there's a few smaller things too. I'll list them in the original issue.

Sounds like a good plan 😁

[seanmonstar]

Thanks for starting this! Eliza did most of the rest in #2317, and the one last tweak was finished in #2319.