PDF plugin hooks

Each plugin could use PDF to manage item sheet generation

A plugin must define the hook :

$PLUGIN_HOOKS['plugin_pdf'][FOO_TYPE]='foo';

And it must provides 2 hook functions :

/**
 * Hook : options for one type
 * 
 * @param $type of item
 * 
 * @return array of string which describe the options
 */
function plugin_foo_prefPDF($type) {
    global $LANG;
    switch ($type) {
        case FOO_TYPE:
            return array("Option bar1", "Option bar2");
    }
    return false;
}
/**
 * Hook to generate a PDF for foo type
 * 
 * @param $type of item
 * @param $tab_id array of ID
 * @param $tab of option to be printed
 * @param $page boolean true for landscape
 */
function plugin_foo_generatePDF($type, $tab_id, $tab, $page=0) {
    if ($type==FOO_TYPE) {
        plugin_foo_generalPDF($tab_id, $tab, $page);    
    }
}

PDF plugin will handled user's pref, item tab and massive action.