Eptarch

Hey, that's great! Just dropping in to say two things: 1. It will probably be good to add tests to [resizer_test.go](https://github.com/h2non/bimg/blob/master/resizer_test.go) and [vips_test.go](https://github.com/h2non/bimg/blob/master/vips_test.go) 1. I am really looking forward for...

I think our case may provide the third solution. We have images with known width (1200 px), but unknown height (anywhere between 500 and 3600 px) and it needs to...