Moved functions.py from templates to theme root

As pointed by @tcg, the functions.py file is more suited to be located
in the theme root.

pelican/generators.py

@@ -64,11 +64,12 @@ class Generator(object):
             extensions=self.settings['JINJA_EXTENSIONS'],
         )
         try:
-            theme_functions = imp.load_source('theme_functions', self._templates_path[0]+'/functions.py')
+            theme_functions = imp.load_source('theme_functions',
+                    os.path.join(self.theme, '/functions.py'))
         except IOError:
             theme_functions = None
 
-        if theme_functions and '__export__' in vars(theme_functions):
+        if theme_functions and hasattr(theme_functions, '__export__'):
             for func_name in theme_functions.__export__:
                 self.env.globals[func_name] = getattr(theme_functions, func_name)