Add return type extension for echo key in args array

[IanDelMar]

This PR adds a dynamic return type extension covering the following functions that support an $echo argument inside an $args array with default value true or 1 :

• the_title_attribute()
• wp_dropdown_categories()
• wp_dropdown_languages()
• wp_dropdown_pages()
• wp_dropdown_users()
• wp_get_archives()
• wp_link_pages()
• wp_list_authors()
• wp_list_bookmarks()
• wp_list_categories()
• wp_list_comments()
• wp_list_pages()
• wp_list_users()
• wp_login_form()
• wp_page_menu()

[szepeviktor]

Thank you for your work @IanDelMar!

Please take a look at my WordPress core rewrite and give it a star :)
https://github.com/szepeviktor/WordPress-the-good-parts

[johnbillion]

Nice work!