adding override tests
Added env override tests (and caught a typo)
APP_KEY not AUTH_TOKEN... duh!
Added app-id and app-secret config options
Added a customized configuration error and cleaned up spacing in the
usage string.
Added config options to documentation
Merge pull request #26 from egravert/add-app-key

Added Config settings for app id,  key, and secret
Merge remote-tracking branch 'upstream/master' into combine-servers

Conflicts:
	config/config.go
	config/usage.go