Initial steps for moving to using Mail in place of RMail. Also various
Ruby 2.0.0 compatability fixes have been made.

…ndex

…RMail ids and we do not need to migrate

Conflicts:
	lib/sup.rb
	lib/sup/maildir.rb
	lib/sup/mbox.rb
	lib/sup/message.rb
	lib/sup/message_chunks.rb
	lib/sup/modes/edit_message_mode.rb
	lib/sup/util.rb
	sup.gemspec

…ngleton

As suggested by Martin Bähr.

* develop:
  history: bundler and threadkilling
  travis: drop 2.1.0 testing
  fix travis. The rake task to build a gem is now 'rake build'
  sup.gemspec: Standarise the Gemspec
  Merge #300: sup-tweak-labels sync back unless specified otherwise
  sup-sync: error msg on :update
  thread_view_mode: Kill a message (and next, prev etc..)
  history: new :with_attachment
  Add new colormap for attachment sybol with sane fallback for existing colorschemes.
  prepare for 0.17.0
  history: bugfixes
  ctrl-n, ctrl-p: don't close message if there is no next one
  completion-mode: correctly set completion character
  async edit: history
  async edit: automatically launch async hook
  async: option for always async

Conflicts:
	sup.gemspec