{:parse {:interpose ""}} violates least surprise

[kkinnear]

The default interpose value for {:parse-string-all? true {:interpose true}} should give you one blank line between expressions, and :interpose "\n" should give you none, but it doesn't work out that way. Ultimately the goal is to:

1. Have a reasonable default (e.g., one blank line between expressions)
2. Enable people to have as many (or no) blank lines between expressions.

Can't do that today. Need to fix it so you can.