Check the included LICENSE.md file for the license associated with this code.
The project includes a .sln and 2 .csproj files which will create a Netduino 2 program and a class library. Both the .sln and .csproj are compatible with Visual Studio 2013 and later.
I wrote this library a long time ago and only recently dusted it off. I seem to remember getting a reference for the I2CDevice from somewhere, but I cannot track down where I found it. I think I've modified it enough to avoid any copyright issues, and I remember it being open sourced. If you are the original author or recognize your work please let me know for proper attribution.
This branch provides an example on how to utilize Events (as opposed to a loop) to monitor button press feedback. It allows Main() to exit so that other events (such as Serial Port Data Recieved) can be fired. Simply solder a wire to Pin 20 (INTA) of the MCP23017 chip and then connect it to a digital I/O port on the netduino. The example code uses GPIO_PIN_D10 to register the interrupt and read the data containing which button was pressed.