Require Only One Module

[wbotelhos]

First, thanks for this great gem!

Is there any way to require only ruby-vips? I was thinking that maybe is a good idea do not include both libs, so we don't need to install it on the docker image. If a conditional require dependency is not possible, maybe separates it in two different gems like:

image_processing_vips
image_processing_mini_magick

[janko]

In the upcoming major version, I will demote MiniMagick and ruby-vips to optional dependencies. This means people will have to add MiniMagick or ruby-vips to their Gemfiles, depending on which backend they want to use.

I will also remove the ImageProcessing::{Vips,MiniMagick} autoload, so that people need to require image_processing/{vips,mini_magick} upfront. I believe dependants like Active Storage are currently relying on the autoloading, which is not good, it needs to be eager loaded.