paperTooth (shader module)

The pure math every paperBlocks paper is made of: pb_tooth (felt tooth and grit, by sharpness), pb_fibres (long fibres), pb_weave (a plain canvas weave), pb_rules (ruled lines), pb_foxing (age spots) and pb_keep (how much of a part to keep at a given drawn size). It reads no screen inputs, so the full-frame papers (through paperCore) and the paperSurface material lay exactly the same tooth. Include it after styleKit's skPatterns. Every px argument is drawn pixels per tooth unit, and any part finer than about two drawn pixels fades to its mean, so the tooth never shimmers.