TODO.txt

- Ensure that HTTP headers are properly sanitized (see http://tools.ietf.org/html/rfc2616#section-4.2, http://tools.ietf.org/html/rfc2616#section-6.2, http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html)
- Allow data to have dynamic values when values are callable
- Cache HTML content and header content when data values are not dynamic
- Have the config validate itself, and raise an exception in ::Metadata if config is invalid