Fixes https://github.com/feedjira/feedjira/issues/212

When the Atom parser is deciding which of the <link> elements present holds the URL for the feed, look for a <link> with rel="self". When deciding which is the website URL, if no <link> has type="text/html", return the href value for the last <link> in the XML which is not the feed <link>, if possible.
When Atom parser looks for the feed URL, it looks for link elements with rel="self".

I forgot this change in commit cd60f450d100f3637df535464131f14b4932f765.
Simplified url method in Atom parser

It's functionally equivalent but much cleaner. Added sample feed and
test case for the bug being fixed.
Bump version for 1.2.0
Update CHANGELOG for 1.2.0