ResourceTransformationKey are provided by the different transformation implementations. It identifies the transformation (name) and its configuration (elements). We combine this in a chain with the rest of the transformations with the target filename and a content hash of the origin to use as cache key.
NewResourceTransformationKey creates a new ResourceTransformationKey from the transformation name and elements. We will create a 64 bit FNV hash from the elements, which when combined with the other key elements should be unique for all practical applications.
Value returns the Key as a string. Do not change this without good reasons.