`read` is always non-blocking even when no data is available to read about serialport-rs

[mlsvrts]

Possibly related to #25

I guess that the current solution for 'wait forever' on read would be:

port.set_timeout(Duration::MAX).ok();

[eranknafo2001]

At least in posix systems, it is because of this:

    #[cfg(target_os = "linux")]
    let wait_res = {
        let timespec = TimeSpec::milliseconds(milliseconds);
        nix::poll::ppoll(slice::from_mut(&mut fd), Some(timespec), SigSet::empty())
    };
    #[cfg(not(target_os = "linux"))]
    let wait_res = nix::poll::poll(slice::from_mut(&mut fd), milliseconds as nix::libc::c_int);

from the file: src/posix/poll.rs.

In the case of linux systems, the ppoll timeout parameter needs to be None to block without timeout.
In the case of non-linux systems, the poll's timeout parameter needs to be negative to block without timeout.
In both cases the default timeout of the library (0) will cause to always return without blocking.

[mlsvrts]

@eranknafo2001 Agreed, but I don't think there is any way to express 'no timeout' in serialport-rs (see my comment here) -- so we're left with 'wait for a really long time' as a work-around.

[eranknafo2001]

I created a PR to fix it #50

[DanielJoyce]

Termios is a layer on top of a raw serial port. I think serial port library should just stick to simple support for serial port, and we can write extensions on top. But we shouldn't complicate serial-port-rs.