Port InferenceData conversion code

Author: OriolAbril

pymc3/__init__.py

@@ -40,7 +40,12 @@ def __set_compiler_flags():
 
 from pymc3 import gp, ode, sampling
 from pymc3.aesaraf import *
-from pymc3.backends import load_trace, save_trace
+from pymc3.backends import (
+    load_trace,
+    predictions_to_inference_data,
+    save_trace,
+    to_inference_data,
+)
 from pymc3.backends.tracetab import *
 from pymc3.blocking import *
 from pymc3.data import *

pymc3/backends/__init__.py

@@ -60,6 +60,7 @@
 Saved backends can be loaded using `arviz.from_netcdf`
 
 """
+from pymc3.backends.arviz import predictions_to_inference_data, to_inference_data
 from pymc3.backends.ndarray import (
     NDArray,
     load_trace,