* Removed: array_replace_recursive() to support PHP below 5.3.
* Changed: to use md5() for the error transient name, class name + page slug, to prevent WordPress from failing to retrieve or save options for the character lengths exceeding 45 characters.
* Changed: to echo the value in a user-defined custom field type.
* Added: the *pre_html* and *post_html* keys for input fields that adds extra HTML code before/after the field input and the description.
* Added: the *value* key for input fields that precedes the option values saved in the database.
* Added: the *disable* key for input fields to add disabled="Disabled".