Support printing newlines in variable repr/str display

A useful option enable printing newlines for variable display for str/repr.

Right now if a variable contains newlines they are shown as ?. So it looks like the user typed `repr(var)` in interactive mode. For example:
`a {? b? }?`

It would be handy if the newlines could be printed. So it would look the same as just typing `var` in interactive mode (or `print repr(var)`). For example:

```
a {
b
}
```