Do not report features with unknown support as unsupported

[lefta]

For now, when support for a feature is not in the database, it is reported as unsupported. This messes the output for some browsers which lack some data ( especially with #16 ).

IMHO, the perfect way to handle it would be to report them as unknown instead of unsupported. In the overview, I would see grey boxes (or any color you want) to report that every known feature is supported, but some are still undocumented. And in the details list, we would need a way to report if the feature is unsupported or just undocumented, maybe with a color or an icon.