Add pretty-printting of settings as dict if using IPython shell

Suggested by @Digenis
see http://ipython.readthedocs.org/en/stable/api/generated/IPython.lib.pretty.html?#extending

scrapy/settings/__init__.py

@@ -4,6 +4,7 @@
 import warnings
 from collections import MutableMapping
 from importlib import import_module
+from pprint import pformat
 
 from scrapy.utils.deprecate import create_deprecated_class
 from scrapy.exceptions import ScrapyDeprecationWarning
@@ -388,6 +389,12 @@ def copy_to_dict(self):
         settings = self.copy()
         return settings._to_dict()
 
+    def _repr_pretty_(self, p, cycle):
+        if cycle:
+            p.text(repr(self))
+        else:
+            p.text(pformat(self.copy_to_dict()))
+
     @property
     def overrides(self):
         warnings.warn("`Settings.overrides` attribute is deprecated and won't "