allow streaming of jinja templates for reduced page load start latency (e.g. for large lists)

def stream_template(template_name, **context):
    ''' allow streaming of jinja templates for reduced page load start latency (e.g. for large lists) '''
    app.update_template_context(context)
    t = app.jinja_env.get_template(template_name)
    rv = t.stream(context)
    rv.enable_buffering(5)
    return rv