Removed OStatus::Thread.

Functionality just returns an empty OStatus::Entry structure when a
Thread is found. I will add an #update method that will return a newer
entry based upon the url of that entry which can be used to retrieve the
thread entry.
Adds HTTPS support to feed/entry retrieval.
Adds source field to Entry.
Removed OStatus::PortableContacts.

The information is just added on to Author and just output in XML as
PortableContacts poco:blah namespace. No need to expose that
specification to anybody who just wants to represent a person.