Added a custom package to inject datetime in templates

Modified blog pagination filter to show only posts which pubdate is
less or equal than today's date.

packages/template-datetime/lektor_template_datetime.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+import datetime
+
+
+from lektor.pluginsystem import Plugin
+
+
+class TemplateDatetimePlugin(Plugin):
+    name = u'template-datetime'
+    description = u'Adds the datetime package to the template context'
+
+    def on_process_template_context(self, context, **extra):
+        context['datetime'] = datetime