Finish up work on annotated tags

Created by: asedge

After screwing up the first attempt at this PR, here it is again.

• Fixed up JSON response for tags, now includes the message and changed API doc to reflect the change.
• Re-added spec for annotated tag creation with the API. Can now verify the message.
• Added tag's message to tag list. I think the style used for the message can be improved, maybe it's not desirable to be displayed at all. I'm hoping for a suggestion here: