Minor reorganizing of register_meta_box checks
Added use of get_fields argument for dynamic field generation
Added since tag documenting last change
Restructured save handling, added use of get_fields setting
Updated save hook to be passed $args and $meta_box
Added documentation for the $fields callback.
Overhauled extract_value
Added use of extract_value on get_value, fixed make_id, added data-id to edit gallery items.