Auto-scroll truncated text

When text is truncated it should automatically scroll left and right on an interval.

E.g. given the text "Never gonna give you up - Rick Astley"

You would move the truncation offset about 1 character every 500ms until the end is reached (at which point it should reverse).

There should also be a short delay (2 seconds or so) when the truncation offset reaches 0 again.

e.g. (the bar represents the truncation)
```
Never gonna give you up - Rick Astley
| ---------------- |
```
rendered: `Never gonna give...`

**~500ms later:**
```
Never gonna give you up - Rick Astley
| ---------------- |
```
rendered: `ever gonna give ...`

**~500ms later:**
```
Never gonna give you up - Rick Astley
| ---------------- |
```
rendered: `ver gonna give y...`

... etc