thrift.el: fix formatting for package.el compatibility [THRIFT-2142]

The standard `package.el` library used in recent Emacsen requires package source files to conform to certain formatting conventions, since it parses metadata out of them.

These changes will allow `thrift.el` to be added to popular elisp package
repositories such as Marmalade and [MELPA](http://melpa.milkbox.net/).