This folder's subfolders contain extensions which modify the transitfeed
package to adapt it to more specific requirements.

Each subfolder has to be a valid Python module and its name should be the same
as the extension name, e.g. googletransit. This name will be used to import the
extension as a Python module. The Python module must expose at least the
GetGtfsFactory() method at the module level. All classes from the transitfeed
module, inheriting the GtfsObjectBase and being instantiated via the GtfsFactory
can be extended (overridden). Extended classes can be registered in the
GtfsFactory via the UpdateClass(). New classes can be registered in the
GtfsFactory via the AddMapping() method.

You can tell FeedValidator to use an extension while validating a feed. Running
FeedValidator with an extension is done with the "--extension" option, e.g.
./feedvalidator.py <feed_filename> --extension extensions.<extension_name>

If you are developing your own program, and want to use an extension from your
code, you can do so by calling extensions.<extension name>.GetGtfsFactory()
instead of transitfeed.GetGtfsFactory().
