Inline documentation improvements for wp-includes/comment-template.php.

Changes include:
- Existing phpdoc block improvements
- Inclusion of defaults for optional parameters
- Hash-notated argument arrays
- Removal of unnecessary or redundant tagging.

Also standardization of int|WP_Post function parameters.

These changes clear the way toward less redundancy for hook docs in a future ticket.

Still left: Fully documented arguments in `comment_form()` and a pass through Walker_Comment.

See #20495. See #25388.

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git-svn-id: http://core.svn.wordpress.org/trunk@25485 1a063a9b-81f0-0310-95a4-ce76da25c4cd