allows upstream to override credentials. fixes #18
remove superenv from core lib, bins use it and set credentials via API
--help flag always shows help and exits.
Ignore NoEcho params that come off existing stack. Fixes #26.
Merge branch 'master' of github.com:mapbox/cfn-config into cred-override

Conflicts:
	bin/config.js
	bin/create.js
	bin/delete.js
	bin/info.js
	bin/update.js
Document setCredentials()
Merge pull request #22 from mapbox/cred-override

Allow upstream to override credentials
Merge branch 'master' into smart-delete
use describeStacks instead of listStacks, also don't say you deleted something if you didn't