complete all introductory documentation, except for the Easy Patterns

section
Also, removed some stray debug lines and added a printed newline
inbetween prompt and output

src/bin/main.rs

@@ -112,8 +112,8 @@ fn main() -> ! {
         let user_doc = rl.read_line(&readline_prompt).unwrap();
         match user_doc {
             Signal::Success(line) => {
+                println!(""); // add a new line before output gets printed
                 let l = line.as_str().to_owned();
-
                 match lex(&l) {
                     Ok(a) => match eval(&a, &mut syms) {
                         Ok(a) => println!("{}", a),