Unify the uses of "urls" vs "URLs".

Use "URLs", which is more prevailing in the source code.

examples/blueprintexample/simple_page/templates/pages/layout.html

@@ -4,7 +4,7 @@
   <h1>This is blueprint example</h1>
   <p>
     A simple page blueprint is registered under / and /pages
-    you can access it using this urls:
+    you can access it using this URLs:
   <ul>
     <li><a href="{{ url_for('simple_page.show', page='hello') }}">/hello</a>
     <li><a href="{{ url_for('simple_page.show', page='world') }}">/world</a>

flask/helpers.py

@@ -264,7 +264,7 @@ def external_url_handler(error, endpoint, values):
                            'executed when application context is available.')
 
     # If request specific information is available we have some extra
-    # features that support "relative" urls.
+    # features that support "relative" URLs.
     if reqctx is not None:
         url_adapter = reqctx.url_adapter
         blueprint_name = request.blueprint
@@ -284,7 +284,7 @@ def external_url_handler(error, endpoint, values):
         external = values.pop('_external', False)
 
     # Otherwise go with the url adapter from the appctx and make
-    # the urls external by default.
+    # the URLs external by default.
     else:
         url_adapter = appctx.url_adapter
         if url_adapter is None: