allow_lossy improvements?

[bdarfler]

Hi @toy. In #65 (comment) you mentioned using :allow_lossy in pngquant and jpegoptim but it looks like it has only been implemented for jpeg-recompress. Is this an oversight or are the defaults for pngquant and jpegoptim lossless? I'd be happy to make a PR to either add in support for :allow_lossy or maybe to document this better in the README.

[toy]

Hi Benjamin. I just did not get to implementing this in other workers. A bunch of thoughts further :)

By default image_optim is lossless and my idea was to block workers (as it is done for jpeg-recompress) or options (max_quality for jpegoptim, quality for pngquant) if :allow_lossy is not true.
In lossless mode option values making worker lossy can be intercepted in init class method or option block and either fail or show warning and return default value.
Not sure about different default value in lossy mode.
Also max_quality option of jpegoptim is partially redundant as jpeg-recompress should do much better job of lossy reduction of jpeg.

[toy]

@bdarfler Yesterday I've added ignoring of lossy options and released new version.

[bdarfler]

Cool! Thanks!