Fixes for default arguments in general_template.php

[sirzooro]

• updated Inline Docs - added information that arguments are optional where necessary;
  
• added array() as default value for feed_links() and feed_links_extra() (current description for them is "Optional arguments". If someone will call them directly from theme without passing argument, php will generate warning).

(In [12687]) phpdoc updates. Props sirzooro. fixes #11853