More frets in viewport about react-guitar

[4lejandrito]

Hi @mrclay!

Thanks for your suggestions:

1. The way I'd do this is using the Theme. We can add a new property to the fret object (something like width) and allow customizing it from there.
2. I think if we make the width property from point 1 a function that receives the fret number we can implement variable width frets.
3. Maybe we can expose a function in react-guitar that converts from shorthand to array of numbers and use it...

You can borrow anything from react-guitar, I'd be very happy 😄.

Feel free to have a go at implementing any of those things yourself. Otherwise let me know and I'll have a go at the weekend.

Thanks!