Added %RATINGS_PLURAL% variable for singular or plural words

Modified the wp-postratings.php and postratings-templates.php files to add a %RATINGS_PLURAL% variable.

%RATINGS_PLURAL% will add an "s" if ratings are not equal to 1. Currently the word "votes" displays as:

1 votes
2 votes
etc.

By adding the %RATINGS_PLURAL% variable after "vote" (vote%RATINGS_PLURAL%), the output will now change to:

1 vote
2 votes
etc.