message: Impl Display for account ledger error and remove unused variant
diff: use crate::value::*;
  use imhamt::{Hamt, InsertError, UpdateError};
  use std::collections::hash_map::DefaultHasher;
  +use std::fmt::{self, Display, Formatter};
  use std::hash::Hash;
  /// Possible errors during an account operation
  @@ -14,12 +15,26 @@ use std::hash::Hash;
  pub enum LedgerError {
  NonExistent,
  AlreadyExists,
  - MismatchCounter,
  NeedTotalWithdrawal,
  NonZero,
  ValueError(ValueError),
  }
  +impl Display for LedgerError {
  + fn fmt(&self, formatter: &mut Formatter) -> Result<(), fmt::Error> {
  + match self {
  + LedgerError::NonExistent => "Account does not exist",
  + LedgerError::AlreadyExists => "Account already exists",
  + LedgerError::NeedTotalWithdrawal => {
  + "Operation counter reached its maximum and next operation must be full withdrawal"
  + }
  + LedgerError::NonZero => "Removed account is not empty",
  + LedgerError::ValueError(_) => "Value calculation failed",
  + }
  + .fmt(formatter)
  + }
  +}
  +
  impl From<ValueError> for LedgerError {
  fn from(e: ValueError) -> Self {
  LedgerError::ValueError(e)
  