Basic Chord class created

Hi,

I saw this repo and decided to try and help out with it. I have zero practical team git experience and have never done this pull request thing before; let me know what's wrong with what I've done. 

This is basically just a way to create basic triads and storing the Note objects in an internal list in the Chord object; there's a lot of functionality that can still be added of course but this is my first go at implementing them;let me know what you think.