Add async select syscall

[yunwei37]

• Add async select syscall
• add time out support in async for poll and select
• add test for poll and select
• add doc

[coveralls]

Pull Request Test Coverage Report for Build 226239204

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 128 of 140 (91.43%) changed or added relevant lines in 5 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+1.7%) to 49.039%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
linux-syscall/src/file/poll.rs	107	119	89.92%

Files with Coverage Reduction	New Missed Lines	%
linux-syscall/src/file/poll.rs	2	85.56%
linux-syscall/src/lib.rs	2	48.78%

Totals
Change from base Build 220845524:	1.7%
Covered Lines:	7401
Relevant Lines:	15092

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💛 - Coveralls

[wangrunji0408]

Thanks!

In the future, we may use the select! macro to simplify the implementation of select, poll and timeout.