Reorganize test running

- Moves all TestML related functions to TestMLTiny, including
  testing coderefs

- Eliminates TestMLRun in favor of testml_run_all_tests
  in TestMLTiny

- Genericizes test_yaml_json so that it might be useful for testing
  how alternate back-ends work

- .tml files are run in a subtest with a test plan based on the number
  of blocks