PEP8 styled files in docs/ (#10713)

### Summary
Modify `docs/autogen.py` so it complies to PEP8 line length rule (line length = 85).

### Related Issues

### PR Overview

- [ ] This PR requires new unit tests [y/n] (make sure tests are included)
- [ ] This PR requires to update the documentation [y/n] (make sure the docs are up-to-date)
- [X] This PR is backwards compatible [y/n]
- [ ] This PR changes the current API [y/n] (all API changes need to be approved by fchollet)

docs/autogen.py

@@ -383,7 +383,10 @@ def get_class_signature(cls):
     except (TypeError, AttributeError):
         # in case the class inherits from object and does not
         # define __init__
-        class_signature = clean_module_name(cls.__module__) + '.' + cls.__name__ + '()'
+        class_signature = "{clean_module_name}.{cls_name}()".format(
+            clean_module_name=clean_module_name(cls.__module__),
+            cls_name=cls.__name__
+        )
     return post_process_signature(class_signature)
 
 
@@ -442,7 +445,8 @@ def count_leading_spaces(s):
 
 def process_list_block(docstring, starting_point, leading_spaces, marker):
     ending_point = docstring.find('\n\n', starting_point)
-    block = docstring[starting_point:None if ending_point == -1 else ending_point - 1]
+    block = docstring[starting_point:(None if ending_point == -1 else
+                                      ending_point - 1)]
     # Place marker for later reinjection.
     docstring = docstring.replace(block, marker)
     lines = block.split('\n')
@@ -590,9 +594,11 @@ def render_function(function, method=True):
     subblocks = []
     signature = get_function_signature(function, method=method)
     if method:
-        signature = signature.replace(clean_module_name(function.__module__) + '.', '')
+        signature = signature.replace(
+            clean_module_name(function.__module__) + '.', '')
     else:
-        signature = signature.replace(clean_module_name(function.__module__) + '.', '', 1)
+        signature = signature.replace(
+            clean_module_name(function.__module__) + '.', '', 1)
     subblocks.append('### ' + function.__name__ + '\n')
     subblocks.append(code_snippet(signature))
     docstring = function.__doc__
@@ -675,7 +681,8 @@ if __name__ == '__main__':
         if os.path.exists(path):
             template = read_file(path)
             assert '{{autogenerated}}' in template, ('Template found for ' + path +
-                                                     ' but missing {{autogenerated}} tag.')
+                                                     ' but missing {{autogenerated}}'
+                                                     ' tag.')
             mkdown = template.replace('{{autogenerated}}', mkdown)
             print('...inserting autogenerated content into template:', path)
         else:

pytest.ini

@@ -14,8 +14,6 @@ norecursedirs= build
 
 pep8ignore=* E402 \
            * E731 \
-           docs/autogen.py E501 \
-           docs/__init__.py E501 \
            examples/addition_rnn.py E501 \
            examples/antirectifier.py E501 \
            examples/babi_memnn.py E501 \