Adds CONTRIBUTING.md file, with contribution guidelines.
Adds 'suppress_filters' => 'false' to all calls to the get_post() function.
Adds a check for the presence of a nonce prior to running the meta box save logic.
Replaces add_post_meta() with update_post_meta() when saving conditions. Avoids possibility of empty records being added to the database.
Optimises ajax_toggle_advanced_items() method.
Adds missing esc_html() and esc_attr() functions in the meta_box_content() method.
Fixes incorrect placement of 'if' in the ajax_toggle_advanced_items() method.
Adds missing esc_html() around taxonomy term labels.
Removes requirement of 'show_ui' parameter for retrieving taxonomies. Fixes #3.
Adds attempt to calculate the maximum number of sidebars required in order to determine the best sidebar to replace each registered sidebar region.