DOC: some versionadded notes

Add some `versionadded` and fix some existing notation that uses formatting that sphinx doesn't understand.  `assert_allclose` seems to have been added in 1.6 and subsequently backported to 1.5 so I am listing it as 1.5.  In practice I look at these annotations in the numpy docs so that I can decide whether or not I can use functions in projects that support e.g. numpy 1.5.1+