modified README. run only on > 3.14

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
modified benchmark

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
add submit_flush_request() to request flushing on worker thread

without this, barrier_plog_writes() causes deadlock

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
don't free plog things when type=0

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
add wbdebug() lines

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
remove test 2 from the regression test because it is too slow

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>