message: add way to destroy a blockchain
diff: @@ -51,6 +51,10 @@ impl Blockchain {
  blockchain
  }
  + pub unsafe fn destroy(self) -> ::std::io::Result<()> {
  + ::std::fs::remove_dir_all(self.dir)
  + }
  +
  /// load the blockchain
  pub fn load(root_dir: PathBuf, name: String) -> Self {
  let dir = config::directory(root_dir, &name);
  