Upgrade the postmark gem dependency to ~> 1.0.x.
Move RSpec to the Gemfile.
Remove attachments fix from the Rails 3 installation process.
Remove a reference to rails 3 from the method name, since postmark-rails also supports rails 4.
Require json in spec helper.
Fix unit tests.
Remove pattern option from RSpec configuration.
Add basic integration tests.
Add TestMailer#message_with_attachments.
Add unit tests for a message with attachments.
Add integration tests for a message with attachments.