Pyusbiss

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* Tidied up README.md

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* Refactored USB-ISS driver using property decorator
* Updated SPI driver to use updated USBISS driver
* Fully documented SPI driver
* Some fixes

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* Refactored the codebase so that each protocol can be controlled by its own
class. This means a breaking change in the interface.
* SPI and USBISS support only in this release with updated usage.
* Added SPI tests.
* Updated README.rst with new interface.

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* Changed SPI mode scheme to official SPI scheme rather than USB-ISS scheme.
* Clarifies project mission in README.rst

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* functional usbiss control and spi control.

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* Initialised project