Denon PMA-770 (and others) Arduino Control

# About

This project ultimately seeks to be a "logic control" modification for a 
Denon PMA-770; allowing one to do things like change inputs, volume, 
balance, and tone using a remote control.

But that's a long ways down the road; so right now it's goal is to drive 
relays and a display to replace the source input switches and input 
display. I am designing it around the aforementioned Denon; but it can 
obviously work for other units with some modification. 

Schematics and pictures up later.

# History

```
28-Dec-2019: Initial Version. Just reads five switches and triggers an 
output.
29-Dec-2019: Added a display. Cleaned up code. Made a repository.
````