Relax settings requirements for Slack

* Transitional: branch "gemify" has different, required params
Merge pull request #55 from librato/feature/slack-alert-transition

Relax settings requirements for Slack
Support arbitrary key/value source names in customer.io
Add explicit test for other payload values
Elide unnecessary fields in the details section of the pd payload
Revert "Elide unnecessary fields in the details section of the pd payload"

This reverts commit 102bf4b9beed18ec371898bbc9e9b495ff09914d.

- Did not mean to push to the gemify branch
Elide unnecessary fields in the details section of the pd payload
Use a property whitelist for fields we include in the PD payload
Merge pull request #62 from librato/feature/slim-pd

Slim down the PagerDuty payload
Merge branch 'gemify'

Conflicts:
	services/slack.rb
	test/slack_test.rb
Bump to 2.0.0 for gem release
Update jeweler, then fix deps to shut jeweler up
Rake task to release to packagecloud.io
Regenerate gemspec for version 2.0.0
Make jeweler shut up about deps
Fix deps so jeweler will shut up for realz
Merge remote-tracking branch 'origin/gemify'
Version bump to 2.1.0
Regenerate gemspec for version 2.1.0
Fix gem artifact path for release