jinja2 2.6+ required

[hmmbug]

Thanks for a great set of macros! I'd like to recommend a minor addition to the documentation. Please could you specify jinja2 2.6 or newer is required as older versions give cryptic messages like this from ansible:

fatal: [myserver] => {'msg': "TemplateAssertionError: no test named 'mapping'", 'failed': True}

or this from other python scripts where the full stack track can be seen:

Traceback (most recent call last):
  File "./validate.py", line 24, in <module>
    t = Template(template_text)
  File "/usr/lib64/python2.6/site-packages/jinja2/environment.py", line 625, in __new__
    return env.from_string(source, template_class=cls)
  File "/usr/lib64/python2.6/site-packages/jinja2/environment.py", line 563, in from_string
    return cls.from_code(self, self.compile(source), globals, None)
  File "/usr/lib64/python2.6/site-packages/jinja2/environment.py", line 448, in compile
    self.handle_exception(exc_info, source_hint=source)
  File "<unknown>", line 13, in template
jinja2.exceptions.TemplateAssertionError: no test named 'mapping'

Linux distros such as CentOS 6.6 install older versions (eg. 2.2.1) with the EPEL ansible 1.9.1 package.