Parses the results from `cat-file -p`

data - String tag object data. Example:

         object 7bcc0ee821cdd133d8a53e8e7173a334fef448aa
         type commit
         tag v0.7.0
         tagger USER <EMAIL> DATE

         v0.7.0

Returns parsed Hash. Example:

  {:message => "...", :tagger => "bob", :tag_date => ...}