Manual test used here:
abc
```lines
{"p1":{"y":72,"x":82},"mode":"line","p2":{"y":29,"x":169}}
```
def
```lines
{"p1":{"y":36,"x":56},"mode":"line","p2":{"y":59,"x":163}}
```
```lines
```
ghi
jkl
Hitting page-down moves the cursor from abc to ghi. The 'ghi' line
should be fully visible on screen.
Still some limitations. The text cursor has to be visible on screen, so
if you have a long series of drawings without intervening lines of text
you won't be able to scroll through them all.