create DSL for declaring the Metrics in a Mailer - closes #7

removes the notion of Reports
add summary, description and homepage to gemspec - fixes #26
Merge pull request #33 from afeld/metric-dsl

@fancyremarker => make Metric inclusion in a Mailer declarative
Merge pull request #34 from afeld/gemspec

@anyone => add summary, description and homepage to gemspec
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