code: function validateFields ( fldsMeta, fldsValue ) {
          return reduce(function ( acc, fldMeta, fldID ) {
              var value  = getOrNull( fldsValue, fldID )
                , errors = validateField( fldID, fldMeta, value );
              return t.merge( acc, errors );
          }, {}, fldsMeta );
      }
docs: Calculates validity of the array of fields.
  @param {Object[]} fldsMeta - array of metadata.
  @param {Object[]} fldsValue - map with fields value.
  @returns {Object} - {
  %fieldID%: [ %failed_validators% ],
  ...
  }