Rename ItunesRssItem#guid to #entry_id to follow all other item types
Make #169 backwards-compatible

We probably never meant for `guid` to be used, so this is probably a
bug, but its been a part of the public interface for so long that I
don't feel right changing it with just a bug-fix release.

Instead, I'm going to treat this as a feature and this commit makes it
backwards-compatible. Once we go 1.0, I'll drop guid altogether.
Add spec for Feed#setup_easy

There are a couple open issues that involve supporting additional
options to Curl, but there wasn't any test coverage. This commit adds
some basic coverage and sets me up to be able to add those options with
a clear conscience.
add ssl_version and ssl_verify_peer options for curl
Added cookie jar support.
Docs and specs for curl ssl opts from #98 and #156

Also closes #154 and #168.
Bump version for 0.3.0
Update CHANGELOG for 0.3.0