message: Add description of module `c_simple_ast_builder`
diff: //! This module is for recovering SimpleCAST from RadecoFunction.
  +//!
  +//! Usage of this module is to call `c_simple_ast_builder::recover_simple_ast(rfn)`
  +//! where `rfn` is an instance of `RadecoFunction`, the function returns an instance of
  +//! SimpleCAST and we can obtain higher level representation than Radeco IR.
  use std::collections::{HashMap, HashSet};
  use frontend::radeco_containers::RadecoFunction;
  