Support io_uring for Linux IO

[dongx-psu]

In the current version, we observe a performance degrade on Linux version due to the usage of libaio on async IO handling. It has been a known issue that libaio is not very efficient.

Recently, io_uring is released with Linux kernel 5.1, which advertise to be a high performance aysnc IO library. We should try it and see if we can improve linux version performance by replacing libaio with it.

[dongx-psu]

More details for io_uring can be found here:

http://kernel.dk/io_uring.pdf