Automatically enable Tup mode for files named ‘tup.config’

This is the name of the file Tup looks for when building variants,
meaning users will be working with this file.  So we should
automatically enable Tup mode for it.
Mention in the main comment that ‘tup.config’ files enable Tup mode
Highlight ‘preload’ like the other rest of the keywords

This fixes an omission, as ‘preload’ is a Tup keyword and thus belongs
in the tup/keywords-regexp list.
Fix a typo in a comment for tup/font-lock-definitions
Update copyright notice in the source code for 2013
Add meta information in the source header for MELPA and Marmalade