Fixes mixed tabs/spaces in index.html and use UTF-8

Loading d3.v3.js throws a hissy fit if you don't use UTF-8 in the HTML document (or somehow force the JS to load with UTF-8) because it contains the definition:

```js
var π = Math.PI, τ = 2 * π, halfπ = π / 2, ε = 1e-6, ε2 = ε * ε, d3_radians = π / 180, d3_degrees = 180 / π;
```

because using Greek characters as variable names is hilarious.