File io optimization

Memory pipes are fifo structures which for the most part behave like normal files but are much faster due to the fact that the data is stored in memory and not on the disk.
The two main differences are that pipes do not support seek operations, and that they block the thread. 
To get around the blocking issue, after the two pipes are created, I start a thread that then starts the OCR engine process. This worker thread will stay blocked waiting for input until the main thread opens the pipes and writes the data.
After the main thread writes the input data, it waits for the OCR engine's thread to terminate before reading the pipe. That's done to ensure that all the OCR output has been written to the pipe.

Unfortunately, Tesseract does not support stdin and the PIL.image.save function requires seek operation, thus it can't use the pipe. I tried manually saving the pixels to the pipe, but I'm guessing I'm missing some header because Tesseract thinks the file is invalid. For the time being, I put back the file IO.
You must save the image on disk before starting the tesseract thread !