Make the four different quality parameters customizable
Add a callback "adjustImageParameters" which will add the possibility for anyone to implment their own logic for quality and width calculations
Defaults to the old logic
Fix the reversed Quality settings.
If higher devicepixelratio, lower the quality. This is the same logic as for the WebP quality.
Merge pull request #13 from perosb/master

Add a callback to allow for custom quality/width calculation