Xstools

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* Modified setup.py so pyusb <= 1.0.0b1 is installed as a dependency since the
newer 1.0.0b2 library causes a problem with finding XESS boards on USB ports.

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* Fixed query for XESS USB devices which failed for some USB libraries.

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* Fixed handling of XuLA/XuLA2 boards with old firmware or with the USB-to-JTAG
path disabled.

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* Added command-line and GUI methods for setting/getting flags in XuLA/XuLA2 boards.
* Enabled loading of .bit files into serial configuration flash via gxstools.
* Updated hex file to newest version of the PIC 18F14K50 firmware.
* Added USB-to-serial bridge server between XuLA board and virtual comm port on PC.

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* Added support for upload/download of signed integers to memio methods.

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* Fixed FPGA bitstreams to remove errors during SDRAM upload/download.