Methods to easier customize link url

Hi,

In some frameworks such as DeltaSpike(ViewAccessScoped http://deltaspike.apache.org/documentation/jsf.html#__viewaccessscoped). They need to customize the generated url. In DeltaSpike case to add some parameters.

To acquire this in the Rewrite(rewrite-config-prettyfaces) I have to extend LinkRenderer and copy the full encodeBegin method customizing urlBuilder.build

It would be great to have a protected method only of the point that generate the url to make easy extend and customize it. 

In the pull request I added a protected buildUrl and change urlBuilder to be protected.