Add an option to compress images with lossy minifcations

[grzegorzkrukowski]

Description

Having the option to specify the quality of processed images will be really useful:

Suggested Solution

Right now the --quality parameter affects only ImageAlpha. Adding a few more properties:
--jpeg-quality
--png-quality
--gif-quality
to have control over the quality same as in the ImageOptim application would allow using lossy minification also from the CLI

[taylorkline]

Not strictly a +1, but it's very confusing that the CLI allows this option without requiring ImageAlpha. It's confusing to keep getting "No size savings" regardless of the --quality param specified.