'list_boolean' field type renamed 'boolean', only stores 0 and 1

The 'list_boolean' field type, provided by options.module in Drupal 7, has been replaced / merged in Drupal 8 with the 'boolean' field type (BooleanItem) provided by Core in Drupal 8.

- Unlike the Drupal 7 'list_boolean' field type, which could be configured to use any two arbitrary integers as "on" and "off" values, the 'boolean' field type only stores 0 or 1. The human readable labels for those values can still be configured as field settings:

Drupal 7 settings for 'list_boolean' :

array(
  'allowed_values' => array(12 => 'Please no', 47 => 'Yes, sure'),
)

Drupal 8 settings for 'boolean' :

array(
  'on_label' => 'Yes, sure', // will be stored as 1
  'off_label' => 'Please no', // will be stored as 0
)

- The 'options_onoff' ("Single on/off checkbox") widget has been renamed to 'boolean_checkbox'.
- A dedicated 'boolean' formatter has been added for the field type.