No longer document __init__ attributes without a docstring

Fixes #146
Also fixed duplicates when a property is set in __init__.

autoapi/mappers/astroid_utils.py

@@ -11,7 +11,7 @@ import astroid.nodes
 
 if sys.version_info < (3,):
     _EXCEPTIONS_MODULE = "exceptions"
-    _STRING_TYPES = basestring  # pylint: disable=undefined-variable
+    _STRING_TYPES = basestring  # pylint:disable=undefined-variable
 else:
     _EXCEPTIONS_MODULE = "builtins"
     _STRING_TYPES = str

autoapi/mappers/python.py

@@ -520,7 +520,7 @@ class Parser(object):
             for child in node.get_children():
                 if isinstance(child, astroid.Assign):
                     child_data = self.parse_assign(child)
-                    result.extend(child_data)
+                    result.extend(data for data in child_data if data['doc'])
 
         return result