fix: add notfound() View method; auto-append trailing slash

the latter provides auto-redirect to `/widgets/` when user visits
`/widgets` for example

src/wuttaweb/views/base.py

@@ -73,6 +73,14 @@ class View:
         """
         return forms.Form(self.request, **kwargs)
 
+    def notfound(self):
+        """
+        Convenience method, to raise a HTTP 404 Not Found exception::
+
+           raise self.notfound()
+        """
+        return httpexceptions.HTTPNotFound()
+
     def redirect(self, url, **kwargs):
         """
         Convenience method to return a HTTP 302 response.

src/wuttaweb/views/common.py

@@ -53,7 +53,10 @@ class CommonView(View):
     @classmethod
     def _defaults(cls, config):
 
-        # home
+        # auto-correct URLs which require trailing slash
+        config.add_notfound_view(cls, attr='notfound', append_slash=True)
+
+        # home page
         config.add_route('home', '/')
         config.add_view(cls, attr='home',
                         route_name='home',

tests/views/test_base.py

@@ -3,7 +3,7 @@
 from unittest import TestCase
 
 from pyramid import testing
-from pyramid.httpexceptions import HTTPFound, HTTPForbidden
+from pyramid.httpexceptions import HTTPFound, HTTPForbidden, HTTPNotFound
 
 from wuttjamaican.conf import WuttaConfig
 from wuttaweb.views import base
@@ -31,6 +31,10 @@ class TestView(TestCase):
         form = self.view.make_form()
         self.assertIsInstance(form, Form)
 
+    def test_notfound(self):
+        error = self.view.notfound()
+        self.assertIsInstance(error, HTTPNotFound)
+
     def test_redirect(self):
         error = self.view.redirect('/')
         self.assertIsInstance(error, HTTPFound)