JENA-539
Added code to remove RDFReaders from RDFReaderF
added documentation
fixed some documentation in RDFWriterF
fixed a null ponter error in RDFWriterF

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1536382 13f79535-47bb-0310-9956-ffa450edef68