Add Summarization to Pipelines (#3128)

* passing

* Undo stupid chg

* docs

* undo rename

* delete-cruft

* only import if you have torch

* Dont rely on dict ordering

* Fix dict ordering upstream

* docstring link

* docstring link

* remove trailing comma for 3.5 compat

* new name

* delegate kwarging

* Update kwargs

docs/source/main_classes/pipelines.rst

@@ -61,3 +61,8 @@ QuestionAnsweringPipeline
 
 .. autoclass:: transformers.QuestionAnsweringPipeline
 
+
+SummarizationPipeline
+==========================================
+
+.. autoclass:: transformers.SummarizationPipeline