Create a Microchip MCP23XXX binding

[shaggygi]

Create a binding API for the Microchip MCP23XXX family.

//cc @joperezr @joshfree Please assign this to me. I have a prototype, but trying to work out the kinks and such. This has been a good exercise as it has bought up a few issues/questions. I will post more details and action items as progress is made. Thx

Possible Iterations

• (Add initial Mcp23xxx binding #91) Create initial Mcp23xxx project with tests and samples.
• (Added pin options, abstract class and I2C #130) Separate with Mcp23xxx abstract, create Mcp230xx (I2C), create Mcp23Sxx (SPI).
• (Added pin options, abstract class and I2C #130) Add additional pins for reset and interrupt lines.
• (Added pin options, abstract class and I2C #130) Add ReadBit/WriteBit helper methods.

[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?