Pretty AST

Added SharedHelpers.prettifyAst to print pretty AST.

Note that it still has limitation though if \" is used in the String literal: 

scala> import scala.reflect.runtime.universe._
warning: there were 1 deprecation warning(s); re-run with -deprecation for details
import scala.reflect.runtime.universe._

scala> showRaw(reify(println("This is a \"string\", this is a lonely quote: \"")))
warning: there were 1 deprecation warning(s); re-run with -deprecation for details
res0: String = Expr(Apply(Select(Ident(scala.Predef), newTermName("println")), List(Literal(Constant("This is a "string", this is a lonely quote: "")))))


I don't think that the following is parsable: 

"This is a "string", this is a lonely quote: ""