Collect Buildroot

See and https://buildroot.org/https://git.busybox.net/buildroot/
- The metadata are makefiles as here https://git.busybox.net/buildroot/tree/package/alsa-lib/alsa-lib.mk that are easily to parse. And Buildroot has a target to also display Makefile variables at https://git.busybox.net/buildroot/tree/Makefile?id=3e8e2e0b43b557286cf29f99c8923e5a92a6b44d#n1064

- There is a script to create a JSON index of packages https://git.busybox.net/buildroot/tree/support/scripts/pkg-stats?id=3e8e2e0b43b557286cf29f99c8923e5a92a6b44d

- The Makefile has a target to call this index of packages creation. See https://git.busybox.net/buildroot/tree/Makefile?id=3e8e2e0b43b557286cf29f99c8923e5a92a6b44d#n928 and https://github.com/buildroot/buildroot/blob/2314928cf828ff02939b9c0041964c3ee2dd907d/docs/manual/common-usage.txt#L180

- This JSON metadata dumps of package index is also created in test builds at the bottom of the http://autobuild.buildroot.net/ for the master branch and recent branches: http://autobuild.buildroot.net/stats/