Refactoring for XML output

[42sol-eu]

The issue of project output files and templates both assuming html for everything could use some refactoring.

-- to use as base for rss-feeds

[42sol-eu]

@jan I would make a suggestion in a seperate branch

[42sol-eu]

see https://github.com/42sol-eu/jinja2-rss-generator for my playground.
I think it is not to complicated from the jinja2-generator side.
Instead of using the Environment from the HTML-files in urubu I would use the class Template for the rss-feed-generation. As far as I see it, there will be one rss-feed per project page.

Step 1: understand the rss-specification
Step 2: understand the urubu-data-structure (in info member or processors)
Step 3: implement the prototype in the githup-playground
Step 4: post @jandecaluwe for inspection
Step 5: check for integration into urubu

Sincerely
Felix Häberle

[jandecaluwe]

Feel free to generate pull requests for my review.

[42sol-eu]

Great! Regarding the fact that rss is an xml file, I see two different approaches to solve that:
1 - simply integrate a fixed rss-xml-feed file
2 - integrate a rss-xml-template like the page templates

I would start with the first one - but maybe the second one would be more urubu-style.

What do you think?