#11 images not supported in Atom/RSS

Currently `enrich_msg()` from rss.py is a stripped down and simplified version of `markup()` from microblog.py https://notabug.org/likho/microblog.py/src/rss_1/src/rss.py#L39 https://notabug.org/likho/microblog.py/src/rss_1/src/microblog.py#L83 Also `enrich_msg()` was quickly done to get a working version of feeds. It could also be considered effort duplication to update both functions for any changes in the future. So it's maybe best to adapt `markup()` to export posts for RSS, example: changing relative links to URLs.