custom-background $args enhancement

[frumph]

Looking to have added the rest of the arguments to pass through the $args to include the rest of the appearance -> background parameters including but not limited to position(x/y), repeat and attachment.

add_theme_support('custom-background', $args);

Example:

array(
	'default-color' => '000000', 
	'default-image' => get_stylesheet_directory_uri() . '/images/background-wolfbw.jpg',
	'repeat' => 'no-repeat',
	'position-x' => 'center',
	'attachment' => 'fixed'
);

ie. the repeat position(x/y) and attachment parameters

Main themes even child themes have looks which sometimes need to incorporate fixed or positioning that cannot be set with the current $arguments and it would benefit theme designers to allow those arguments to be passed

20816.diff​ lets themes define background position, repeat, and attachment for their default image in add_theme_support()