UART Read Data Sleep

[samco182]

What's in this pull request?

Adds an usleep invocation right after the read(fd, &buf, buf.count * MemoryLayout<CChar>.stride) call on readData function on the UART.swift class in order to be able to fully read all the available data on the serial port before returning.

Is there something you want to discuss?

For my SwiftyXBee library, I am checking whether there is available data on the serial port right before trying to read actual data from it; in order to avoid blocking my program in case there is no data available. Pretty often, I would be getting this crash: Fatal error: Index out of range: file /home/buildSwiftOnARM/swift/stdlib/public/core/ContiguousArrayBuffer.swift, line 369 when calling uart.hasAvailableData() immediately followed by uart.readData().
By trial an error, I found out that adding a 100ms sleep call right after the actual read method, would allow all the data to be read, so that Array(buf[0..<n]) at the return of the readData method wouldn't cause me a crash. I know it is not the most elegant solution, but it does its job.

Pull Request Checklist

• I've added the default copyright header to every new file.
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• Verify that your code compiles with the currently supported Swift version (currently 4.1.3)
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