Digital Pot MCP4xHVx1

Created by: vector91

Added the following components to the Digital_Potentiometer library:

• MCP41HV51-ST
• MCP41HV51-MQ
• MCP41HV31-ST (alias of MCP41HV51-ST)
• MCP41HV31-MQ (alias of MCP41HV51-MQ)

Their datasheet can be found here: http://ww1.microchip.com/downloads/en/devicedoc/20005207b.pdf The symbols are based on the MCP45HV, I just had to modify the I2C interface in SPI interface and fix other small differences in the pins.

Modified the descriptions of MCP45HV: each alias has the correct number of bits in the description (and not "7/8-bit..." Added datasheet link to MCP45HV.

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