Draft: modtypes: Add pyproject type

This adds a new module type that is for building projects that have a pyproject.toml file.

It uses the build and installer python modules to do this.

I used this as a basic test:

  <pyproject id="meson">
    <branch repo="github-tar"
            version="0.64.0"
            module="mesonbuild/meson/releases/download/${version}/meson-${version}.tar.gz"
            checkoutdir="meson-${version}"
            hash="sha256:c5e27e091c2a35b9049e152a6535045ebbd057253aeb67856de6ecbb7b917bab">
    </branch>
  </pyproject>

Closes #288