isEqual = (a, b) => {
  return a && b && a.hash && a.hash === b.hash
}
Determines whether two entries are equal.
@param {module:Log~Entry} a An entry to compare.
@param {module:Log~Entry} b An entry to compare.
@return {boolean} True if a and b are equal, false otherwise.
@memberof module:Log~Entry
@private