Fix a couple doctests

I still don’t run doctest though since python -m doctest fails on python3 (No module named 'http.client'; 'http' is not a package
) and there are doctest errors in other files.

Author: yonran

remoteobjects/fields.py

@@ -437,11 +437,17 @@ class Link(AcceptsStringCls, Property):
 
     For example:
 
+    >>> from remoteobjects import RemoteObject
+    >>> from remoteobjects.fields import Link
+    >>> class Event(RemoteObject): pass
+    ...
     >>> class Item(RemoteObject):
     ...     feed = Link(Event)
     ...
     >>> i = Item.get('http://example.com/item/')
-    >>> f = i.feed  # f's URL: http://example.com/item/feed
+    >>> f = i.feed
+    >>> f._location
+    'http://example.com/item/feed'
 
     Override the `__get__` method of a `Link` subclass to customize how the
     URLs to linked objects are constructed.

remoteobjects/listobject.py

@@ -88,6 +88,10 @@ class PageOf(with_metaclass(OfOf, type(PromiseObject))):
     new `PageObject` classes that contain objects of a specified other class,
     like so:
 
+    >>> from remoteobjects import RemoteObject
+    >>> from remoteobjects.listobject import PageObject, PageOf
+    >>> class Entry(RemoteObject): pass
+    ...
     >>> PageOfEntry = PageOf(Entry)
 
     This is equivalent to defining ``PageOfEntry`` yourself:
@@ -167,6 +171,9 @@ class PageObject(with_metaclass(PageOf, SequenceProxy, PromiseObject)):
     `PageOf`, with the class reference you would use to construct an `Object`
     field. That is, these declarations are equivalent:
 
+    >>> from remoteobjects import fields, RemoteObject
+    >>> from remoteobjects.listobject import PageObject, PageOf
+    >>> class Entry(RemoteObject): pass
     >>> PageOfEntry = PageOf(Entry)
 
     >>> class PageOfEntry(PageObject):