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

Initial version of 6.x-2.x branch, during a major rewrite. Definitely not finished yet, most of the main features should already work fine though.