Port cook.sh to Rust with Ion recipes

The cook build system (cook.sh in the cookbook repo) should be ported to Rust, with individual recipes as Ion scripts.

Advantages

• This can integrate better with both the pkgutils code and with the installer, since they are all in Rust
• Naturally Redox should prefer our own Ion shell over Bash; if it is worse in some way, let's fix that
• Using Ion also avoid a dependency on Bash when running under Redox (though of course, a lot of C software will still require a bourne shell to compile)
• Ion can be embedded in the program as a library

Other considerations

This involves rewriting cook.sh and all the recipes, so it is a good time to consider other improvements to the way to cookbook works. I think it would be better to not include functions for compiling Rust code by default, but instead have a way to explicitly importing the "template" for Rust recipes. This means an extra line of boilerplate for Rust recipes, but then the C recipes will not need the boilerplate empty functions for test/update just to disable the Rust versions.

Code

I have started this, though there's still much to do: https://github.com/ids1024/pkgutils/tree/cook/src