[tune] Tune Facelift (#2472)

This PR introduces the following changes:

 * Ray Tune -> Tune 
 * [breaking] Creation of `schedulers/`, moving PBT, HyperBand into a submodule
 * [breaking] Search Algorithms now must take in experiment configurations via `add_configurations` rather through initialization
 * Support `"run": (function | class | str)` with automatic registering of trainable
 * Documentation Changes

python/ray/tune/function_runner.py

@@ -12,7 +12,12 @@ from ray.tune.result import TIMESTEPS_TOTAL
 
 
 class StatusReporter(object):
-    """Object passed into your main() that you can report status through."""
+    """Object passed into your main() that you can report status through.
+
+    Example:
+        >>> reporter = StatusReporter()
+        >>> reporter(timesteps_total=1)
+    """
 
     def __init__(self):
         self._latest_result = None