Fix paragraphs: Empty lines separate paragraphs

Somehow i thought it was 2 empty lines rather than 1 - makes more sense this
way... :D

org/util.go

@@ -0,0 +1,19 @@
+package org
+
+func isSecondBlankLine(d *Document, i int) bool {
+	if i-1 <= 0 {
+		return false
+	}
+	t1, t2 := d.tokens[i-1], d.tokens[i]
+	if t1.kind == "text" && t2.kind == "text" && t1.content == "" && t2.content == "" {
+		return true
+	}
+	return false
+}
+
+func isEmptyLineParagraph(n Node) bool {
+	if p, _ := n.(Paragraph); len(p.Children) == 1 {
+		return len(p.Children[0].(Line).Children) == 0
+	}
+	return false
+}