AST dumper should have more new lines in the output

[kevin1]

Probably each expr should be followed by a new line. As we compile bigger and bigger programs, a one-line ast will not be readable.

[kevin1]

here's an example of what ocamldebug does:

sexpr: Sast.expr_typed =
  (Init ("key_sig",
    (Struct ("key_signature",
      [("scale",
        (Arr
          ([(LitFloat 261.63, Ast.Float); (LitFloat 293.66, Ast.Float);
            (LitFloat 329.63, Ast.Float); (LitFloat 349.23, Ast.Float);
            (LitFloat 392., Ast.Float); (LitFloat 440., Ast.Float);
            (LitFloat 493.88, Ast.Float)],
          Ast.Float),
         Ast.Array Ast.Float))]),
     Ast.Type "key_signature"),
    Ast.Mutable),
   Ast.Unit)

i remember there was some ocaml library that makes it easier to print indented stuff.