add new IO expander MCP23017 (2x8bits)

[RREE]

The MCP23017 is similar to the existing MCP23008, it has two ports of 8 pins. Using the latest 12.2 compiler I was nudged to use square brackets for arrays. That might be problem if you want to use it with an older compiler

[Fabien-Chouteau]

Thanks @RREE