[Improvement] use Jinja2 templating scheme

[moutonjr]

Hi, thank you for your work, this is indeed VERY helpful.

This could be great to turn tempalting scheme into Jinja2 one (http://jinja.pocoo.org/docs/2.10/)

The best feature could be case control and iteration with Jinja, just like (in a PPTX file) :

----
Here are the list of to-dos : 

{% for entry in hello.entries %}
-  TODO: {{entry}}
{%endfor%}