Xstools

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* Sped-up memory reads & writes from/to the SDRAM.

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* Removed include in README.rst that caused an error generating the documentation.

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* Specifying the board model on the CLI utilities is now case-insensitive.

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* Now supports pyusb versions 1.0.0a and 1.0.0b.
* The utilities only connect to the USB port when they are actively executing
some function for the attached XESS board. This allows other utilities to
access the board.
* Added drag-and-drop capability for selecting bitstream and hex files.
* A history of bitstream and hex files is maintained.
* Exceptions caused by pyusb on program termination are now caught and filtered out.

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* Removed scripts in bin directory and placed them in the xstools directory.
* Added entrypoints to generate executables for the XSTOOLs scripts.

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* Changed distribution to use readthedocs for documentation.