add more build rewriting commands

[oyvindberg]

• rename project
• combine projects (including moving files)
• add new project
• add cross-compilation to project)

[baovitt]

I'd like to work on this.

[oyvindberg]

Cool! Feel free to ask questions about how to get started or if you're stuck.

Anything in particular you want to try to implement? I think project rename for instance should be an easy start