Issue #181

This fixes the issue, tested with a JSON output and a Turtle output (the latter really shows the difference and correctness). If any more testing needs to be done before this pull request can happen I'd be glad to look if I can be of assistance.
Issue https://github.com/njh/easyrdf/pull/183#issuecomment-40865021
Issue https://github.com/njh/easyrdf/pull/183#issuecomment-40866043
Removed unnecessary empty lines, https://github.com/njh/easyrdf/pull/183/files#r11794647
Issue https://github.com/njh/easyrdf/pull/183
Merge branch 'patch-1' of github.com:coreation/easyrdf into coreation-patch-1

Conflicts:
	test/EasyRdf/Serialiser/RdfXmlTest.php
proper test for empty prefix in rdfxml

refs #183
proper serialization of empty prefix in rdfxml

refs #183
updated changelog
Merged "support for empty prefixes"