Extend to 8 buttons

[cathoderaydude]

Although there are a lot of things I could add to this that would be out-of-scope, I should at least expand it to all eight I/O lines that are available to me now. This should be an hour of work at most.

[cathoderaydude]

This is only remaining open because I need to hook up the other 4 buttons to test my own device. I had tested them earlier in the process but my setup is too fragile to open up to do this right now, so I'll do it once I get the other sample devices I'm ordering.