- moved core formatters into separate file views_rss_core.field.inc

- added new field handler/RSS field formatter for "All taxonomy terms"
- views_rss_core_preprocess_category() no longer used for feed items
- renamed views_rss_core_preprocess_category() to views_rss_core_preprocess_channel_category()
- removed validation on channel <image> element when absolute URL provided
- changed location of raw values in the view object
- updated views_rss_handler_field_user_mail handler to return element as an extended array
- updated template_preprocess_views_view_views_rss() function to handle raw values (especially #markup)
- views-view-views-rss-field.tpl.php modified to handle $markup variable
- updated empty value checks in preprocess functions
- updated view field settings forms
- updated function docs