Issue #3303532 by vpa24, reenaraghavan, DamienMcKenna, Ludo.R: Update Views RSS to be compatible with D10.

Issue #3306849 by DamienMcKenna, adaucyj, lucasbaralm, LeoAlcci, urvashi_vora, juancec, idebr: Update code to follow Drupal coding standards.

Issue #3192236 by jennypanighetti, Suresh Prabhu Parkala: Absolute URLs in data-src or srcset not changed

- updated all preprocess functions to be compatible with format_xml_elements() element format
- removed function views_rss_htmlspecialchars() and all calls to it - this is not done automatically by format_xml_elements()
- updated views_rss_rewrite_relative_paths() to handle multiple elements and arrays of subelements
- updated element definitions to account for updated/removed preprocess functions
- added hook_views_rss_feed_alter()
- element values are no longer going through any theme() function
- removed theme callbacks: views_view_views_rss_fields and views_view_views_rss_field
- removed template files: views-view-views-rss-fields.tpl.php and views-view-views-rss-field.tpl.php

Added option for item <category> element to output terms from hierarchical vocabularies together with their parents (and optionally with vocabulary name) as slash-delimited string

- 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

- keep raw values returned by field formatters in the view and pass them to all preprocess functions
- views-view-views-rss-field.tpl.php template will just print markup without any processing if received in variables

- issue #1440972 by james.williams: fixed "Undefined property" PHP notice from views_rss_plugin_style_fields.inc
- fixed "Undefined property" PHP notice from views_rss_core.module

- removed all theme function
- slightly reorganized element configuration arrays and default configurations
- added new template file views-view-views-rss-field.tpl.php for single feed element
- added Views RSS module build version checking
- other cosmetic changes

Renamed theme functions and template files: "views_view_views_rss_fields" to "views_view_views_rss" and "views_rss_fields_item" to "views_view_views_rss_fields", updated template suggestions for "views_view_views_rss_fields"

Added 4 new hooks and modified old ones, added data caching, added install files, changed view options array structure, moved files and functions around, fixed #1426930, docs, code cleaning

Added "RSS email: with user name" format for email fields, fixed empty <guid> element showing even if not defined

Initial version of 7.x-2.x branch, during a major rewrite. Definitely not finished yet, most of the main features should already work fine though.