Replace all underscores with spaces in Field API keys, for consistency.

Code seen in Drupal's core (text.module):

/** 
 * Implement hook_field_info(). 
 */
function text_field_info() {
  return array(
    'text' => array(
      'label' => t('Text'),
      'description' => t('This field stores varchar text in the database.'),
      'settings' => array('max_length' => 255),
      'instance_settings' => array('text_processing' => 0),
.
.
.

/** 
 * Implement hook_field_widget_info(). 
 */
function text_field_widget_info() {
  return array(
    'text_textfield' => array(
      'label' => t('Text field'),
      'field types' => array('text'),
      'settings' => array('size' => 60),
.
.
.

Why is 'field types' with space but 'instance_settings' with underscore?