create rake task to preview mailers - closes #21
Merge remote-tracking branch 'upstream/master' into preview

Conflicts:
	config.ru
move the test app require-ing into the Rakefile
move all specs under spec/unit/
move require's into files that depend on them
fix MailPreview
ensure that the version is included
Merge pull request #32 from afeld/preview

@dylanfareed => create rake task to preview mailers