Improve `sizes` query handling

[dawaltconley]

Currently several valid sizes query strings are not supported and will throw an error, such as queries using the not keyword, or queries specifying any media type other than all.

I do not intend to handle every valid media query; only those that are useful for responsive images. That said, the not keyword should at least should be supported. Media types may not be necessary, but it may be better to ignore/apply them with a warning rather than throwing an error.

The only supported media features at the moment are min-width, min-height, max-width, and max-height. All others are silently ignored. There may be others worth parsing or others that warrant an error or warning.

[dawaltconley]

The media features I could support (could be validated against device sizes and pixel densities):

• aspect-ratio
• height
• orientation
• resolution
• width

Not sure whether I'll get to all of these, but at least the rest can be safely ignored.

Also, any boolean media features (not specifying a value) can be safely ignored because they will evaluate as true across all devices that we're targeting for images.

[dawaltconley]

All of these are supported in v0.5.0, as well as the not and or keywords. Unsupported media types and other features will throw an error.