Remove external dependencies
Currently the source tree does it contain extern dependencies code like gmp, gc, ffi. While it very useful from the development prospective it does force to download code not necessary and I prefer not to have foreign code in the source tree.
Currently dpkg in debian does not need any of them while ubuntu limitation is just a very old gc, OSX can satisfy all the dependencies with homebrew and windows is another story.
I would like to remove those files from the repo and get them only and only if they are necessary.
There is two strategy, using git modules or getting them with a script. Maybe there is some other strategy that I don't know.
I prefer the latter as it can be used also usable form a distribution tarball.