Modifies sendgrid_unique_args to be accessible at a class level
Allows unique args to be set in both the mailer class and mailer methods. Includes tests. Also gets existing tests running and passing.
Merge branch 'master' of https://github.com/DanOlson/sendgrid into DanOlson-master

Conflicts:
	lib/sendgrid.rb
fixing tests, removing empty filters from header