Make t/* tests stricter: use warnings; -> use warnings FATAL => "all";
Script: implement run() and multiplot(). still debugging.
t/script/run.t: run()'s writer should be very thin. it should NOT filter undef.
Script: multiplot() wraps the writer in the code to detect trailing newline of the written data. Pass t/script/multi.t
t/script/command_block.t: fix the test.
xt/multiplot.t: fix the test. all tests completed.