mKR serializer for Raptor

New files for mKR writer, serializer, tests.
Minimal changes to other programs to add a new language.
I have some questions re: Turtle serializer handling of @base and rdf:nil.
You need to add Makefile.am files and update the top level configure and the tests/Makefile.am to recognize the 'mkr' directories.  This is needed to create a consistent build and for it to work out of GIT.

There also should be tests.