* Add IGpioController.

This allows compositing gpio extenders/multiplexers or any other providers with device drivers.

* Hack to get command line build working

* Address feedback, fix the rest of the projects

* Add a few tests, tweak the projects to play nicer with VS

* Rejigger the abstraction in Mcp23xxx

Change the abstraction some and update the tests to map closer to the implementations. Fix a bug in setting single pin values.

* Change PinValue to struct

Allows easier interop with raw data and enables us to extend with additional functionality. This will avoid having to add additional APIs for convenience and repeated typing of `PinValue == PinValue.High ? 1 :  0`.

Doesn't impact existing enum usage.

Sample usage:

``` C#
    class Program
    {
        static void Main(string[] args)
        {
            PinValue value = true;
            Console.WriteLine($"True is {value}");
            TestApi(0);
            Console.WriteLine($"Equality is {PinValue.High == true}");
        }

        public static void TestApi(PinValue value)
        {
            Console.WriteLine($"PinValue is {value}");
        }
    }
```

* Ok, so you can't switch a struct. :) Bonus now that you don't have to. There is no such thing as an invalid PinValue anymore.

* Added editconfig file

* Beginning of cleaning

* Added summaries and sorted

* Added callback summaries

* Fixed ordering and switch/case based on feedback

* Added editconfig file

* Initial clean scan

* Moved library

* Yet another rename to make consistent

* Removed semicolon

* Renamed to Libraries file

* Added editconfig file

* Cleanup for SPI drivers

* Updated for feedback

* Added editconfig file

* Cleanup for I2C drivers

* Cleanup for I2C drivers

* Updated wording

* Updated for feedback

* Basic cleanup in GPIO files

* Basic comment cleanup in GPIO files

* Removed othing lingering words

* Another round of GPIO cleaning

* Removed a couple more words

* Added readonly and updated casing

* Better method grouping and synced constructor summaries

* implement fallback enumeration for hummingboard - where PWM friendly names are not currently set

* Basic comment cleanup in supporting SPI files

* Added wording from feedback

There was a typo, but also both states can have current depending on hardware configuration.  A Low has ability to sink current.

Adding Raspberry Pi Driver

Adding implementation for the PwmController

* sample/tester cleanup - add a readme and re-org folders

Adding Implementations for UnixSpiDevice

Adding UnixI2cDevice Implementations

Adding Eventing methods to the Unix Driver for Gpio

* Implement the Windows I2C device

* Implement the Windows SPI device

Removing the register address parameter from the read/write methods of SPI and I2C as these aren't general (#41)