Filter title output

Add filter to allow opportunity to avoid or modify appending " (Publication)" to publication title output. 

The nested sprintf() makes me suspect there's a better way to do this… If this filter's in place, perhaps the plugin itself should use the filter to do what sprintf() does here, instead of including it by default. But, this gets the job done.

It will allow me to use this: https://gist.github.com/4527277