Codebug-tether

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- Fixed a bug with set_bulk and updated tests.

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- Fixed bytes error in serial_channel_device -- and/or/bulk commands
work again.
- Added support for analogue inputs and PWM.

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- Fixed error with `set_pullup`. Fixes issue 14.

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- Added UART support.

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- Updated packet layer, better support for bulk commands and AND/OR masks.
- Added extension pin control.
- Added I2C/SPI support.
- Added Colour Tail (WS2812) support.

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- Updated docs.