Graphs

When it prints out the predictions, after each result line, also print a line that shows the confidence percentage and cumulative confidence percentage graphically so you end up with overlapping bar charts.

I don't think I can show what the terminal colours would be in this example, so I'm using symbols to illustrate. Also, the bars should probably be a lot longer than I'm showing here. Maybe as long as the terminal window can fit.

```
2 sprints (4 weeks), 30% confidence (predicted by 296 simulations)
██████░30%░░░░░░░░░░
3 sprints (6 weeks), 68% confidence (predicted by 351 simulations)
████████▒38%▒▒░68%░░
4 sprints (8 weeks), 96% confidence (predicted by 248 simulations)
██████▒28%▒▒▒▒▒▒▒▒▒░96%
5 sprints (10 weeks), 99% confidence (predicted by 25 simulations)
█▒3%▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ 99%
6 sprints (12 weeks), 100% confidence (predicted by 10 simulations)
0%▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ 100%
```