ws
Add mkr turtle writer flag, move it out of internal API.  @base ends in ;

raptor_turtle_writer_flags is now part of internal API with bitflag values
TURTLE_WRITER_FLAG_AUTO_INDENT and TURTLE_WRITER_FLAG_MKR

(raptor_new_turtle_writer): Gains flags arg.

(raptor_turtle_writer_namespace_prefix, raptor_turtle_writer_base):
Lose emit_mkr arg and take it from the turtle_writer struct flags field.

Update mkr tests to end @base lines with ';' like other mkr lines.