Adding RSS feed#4

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cparnot wants to merge 3 commits intokoenbok:masterfrom

Commits on Jan 16, 2015

Fixes some warnings due to deprecated 'ROOT_URL' and 'STATIC_URL'.
cparnot
committed
Adding `rss.xml` page, with the last 20 posts, including content. The site URL needs to be set in the `blog.py` file so the feed contains the full final URLs of the posts.
cparnot
committed
Adding link to the rss feed in the <head> element of the base.
cparnot
committed