Fix descriptions of MongoWriteBatch methods


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@335168 c90b9560-bf6c-de11-be94-00142212c4b1
Revise MongoWriteBatch::add() parameter docs

Rewrote argument descriptions and cross-referenced relevant update() and remove() parameters/options. Also clarified valid "limit" values for delete operations.

https://jira.mongodb.org/browse/PHP-1126


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@335169 c90b9560-bf6c-de11-be94-00142212c4b1