Xstools

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* Added FlashDevice class for reading/writing flash memory devices.
* Made Pic18f14k50 class inherit from the FlashDevice class for flash read/write operations.
* Added routines for reading/writing serial configuration flash on the XuLA and XuLA2 boards.
* Extended xsload.py to enable serial flash uploading and downloading.

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* Fixed xsusbprg.py so it works under linux.
* Fixed USB read/write timeouts so they are dependent upon the amount of data transferred.
* Replaced exit() with sys.exit() in scripts.

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* Added XuLA firmware .hex files for use with xsusbprg.py.
* Fixed xsusbprg.py so it would upgrade XuLA board firmware by default.
* All user-accessible scripts now use xstools_defs.py to get a unified version .
* Added .rules file for USB connections to XESS boards.

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* Replaced bitarray module with pure-Python bitstring module.

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* Fixed so multiple XsUsb objects can share a single USB link to access an XESS board.

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* Changed CR-LF EOL in .py files to LF EOL so linux wouldn't barf.