Create a Microchip MCP23XXX binding

[dotnet]

Create a Microchip MCP23XXX binding

[shaggygi]

@joperezr @joshfree Would it be possible to go ahead and check-in #91? This issue can continue to stay open, though.

This currently works for SPI and has some goodness for a starting layout on binding docs.

I've been thinking about binding fundamentals and understand this will change in future. For example, similar to the Mcp3008 binding and implementing #90, I could see where I/O expanders could implement a similar format. I'm not sure if this would be a type of bus provider, but warrants more thoughts before getting too deep in developing more bindings.

Thx

[joperezr]

@shaggygi I left some feedback on the PR and it looks like you haven't had the chance yet to address/respond to it. Would you mind taking a look?

[shaggygi]

@joperezr I didn't initially hit the resolved buttons. I may have just deleted my comments to your questions by mistake. Could you check again?