Add better documentation, trigger namedtuple.

recipe_engine/run.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Entry point for fully-annotated builds.
 
 This script is part of the effort to move all builds to annotator-based
 systems. Any builder configured to use the AnnotatorFactory.BaseFactory()
 found in scripts/master/factory/annotator_factory.py executes a single
 AddAnnotatedScript step. That step (found in annotator_commands.py) calls
@@ skipping 348 matching lines @@
   def run_step(self, step_dict):
     """
     Runs a step.
 
     Args:
       step_dict (dict): A step dictionary to run.
 
     Returns:
       A StepData object containing the result of running the step.
     """
-    step_config = recipe_api._make_step_config(**step_dict)
+    step_config = recipe_api.StepConfig.create(**step_dict)
     with util.raises((recipe_api.StepFailure, OSError),
                      self._step_runner.stream_engine):
       step_result = None
 
       self._close_through_level(step_config.nest_level)
 
       open_step = self._step_runner.open_step(step_config)
       self._step_stack.append(self.ActiveStep(
           config=step_config,
           step_result=None,
@@ skipping 108 matching lines @@
         results.append(
           loader._invoke_with_properties(
             run_recipe, properties, recipe_script.PROPERTIES,
             properties.keys()))
       except TypeError as e:
         raise TypeError(
             "Got %r while trying to call recipe %s with properties %r" % (
               e, recipe, properties))
 
     return results