Binary build system

This is a first attempt at a binary-build-system. Not using the gnu-build-system was a bit too hard, so I used it after all. The patchelf phase takes a #:patchelf-plan argument that is a list of lists of a binary file name and a list of input names that have to be added as its runpath.

The install phase similarly has an #:install-plan argument that is a list of lists of a base source directory, a list of patterns of files to be installed and a target directory.

I've updated baba-is-you to show haw this works.