Validate response data format

If the API returned data format is neither JSON nor XML, ColdFusion will
throw data parsing errors when failing to convert the JSON string or XML
document. To prevent that, I've added validation rules for both formats
and returned the HTML-escaped response string.

This shouldn't happen very often, but it's good to have it as a safety
net against API downtimes or server rejects like 'HTTP 414 Request-URI
Too Large'
Merge pull request #4 from errorsmith/issue/decodeOutput

Validate response data format