def create_custom_field(field_name, data_type, options=[],
      visible_in_preference_center=true)
      options = { :body => {
        :FieldName => field_name,
        :DataType => data_type,
        :Options => options,
        :VisibleInPreferenceCenter => visible_in_preference_center }.to_json }
      response = post "customfields", options
      response.parsed_response
    end
def create_custom_field(field_name, data_type, options=[],
      visible_in_preference_center=true)
      options = { :body => {
        :FieldName => field_name,
        :DataType => data_type,
        :Options => options,
        :VisibleInPreferenceCenter => visible_in_preference_center }.to_json }
      response = post "customfields", options
      response.parsed_response
    end
Creates a new custom field for this list.
 field_name - String representing the name to be given to the field
 data_type - String representing the data type of the field. Valid data
   types are 'Text', 'Number', 'MultiSelectOne', 'MultiSelectMany',
   'Date', 'Country', and 'USState'.
 options - Array of Strings representing the options for the field if it
   is of type 'MultiSelectOne' or 'MultiSelectMany'.
 visible_in_preference_center - Boolean indicating whether or not the
    field should be visible in the subscriber preference center