Make it so lines.stripMargin(width, true) leaves the first line untouched.
Add a test of parameter-trailing comments.
Allow trailing /*comments*/ to be printed after the node.

For now, trailing //-style comments will still be printed as if they were
leading comments.
Implement Lines.prototype.isOnlyWhitespace.
Require leading comments to be separated from their nodes by whitespace only.

If anything other than whitespace (or other comments) intervenes between
the comment and the node, we assume the comment is a trailing comment.