This patch removes the `clamp0to255` helper function, as well as manual clamping code in `src/core/jpg.js`.
The adjusted constants in `_convertCmykToRgb` were taken from CMYK to RGB conversion code found in `src/core/colorspace.js`.
*Please note:* There will be some very slight movement in a number of existing test-cases, since `Uint8ClampedArray` appears to use `Math.round` (or equivalent) and the old code used (basically) `Math.floor`.