Upgrade version of Tokio to ^1.0.1

[rhdxmr]

This resolves #129 issue.
All example programs work as expected.
All packages of workspace are compiled successfully with stable rust 1.51.0.

[rhdxmr]

And MapIo is marked as deprecated because it implements mio::unix::Evented which is not provided by newer version of mio.

[rhdxmr]

@rsdy I found that the compiling failed under Fedora but succeeded under Ubuntu.
(My local machine uses Ubuntu 20.10 based PopOS)

It seems that AsRawFd trait for RawFd was removed in Apr 2017 by this PR
rust-lang/rust#41035

And the trait was resurrected in Oct 2020 by this PR
rust-lang/rust#76969

A new structure implementing AsRawFd is required to satisfy AsyncFd<T: AsRawFd>.
It's worth avoiding AsyncFd<RawFd> not to cause harm to existing RedBPF users who use rust < 1.48.

[rsdy]

It's worth avoiding AsyncFd not to cause harm to existing RedBPF users who use rust < 1.48.

I don't think it's worth it, as it's quite an old release anyway. Realistically with Rust moving to newer LLVM versions, we're going to need to drop support for these anyway. I think targeting the latest stable compiler is reasonable.

[rhdxmr]

@rsdy OK. That's more convenient way to develop this.
Then the build environment of fedora rawhide is needed to fixed to succeed the compilation?

[rsdy]

I think this is a good first step. Removing deprecations can come at a later stage.

[rsdy]

Actually all the builds fail, and Fedora too. The fact that Ubuntu builds go through is a separate bug in the CircleCI files.

[rhdxmr]

@rsdy Is there something that should be done in order to merge this PR?

[rsdy]

I am currently fixing the CI scripts. I'd prefer if we resolved that issue before merging this PR.

[rsdy]

It looks like I misread the CI output. I'll merge this. Thanks!