function parseRules (validation, rules) {
  if (typeof validation === 'string') {
    return parseRules(validation.split('|'), rules)
  }
  if (!Array.isArray(validation)) {
    return []
  }
  return validation.map(rule => parseRule(rule, rules)).filter(f => !!f)
}
Given an array or string return an array of callables.
@param {array|string} validation
@param {array} rules and array of functions
@return {array} an array of functions