Cache should have subdirectories for e.g formulae and versions #568
Description
The HOMEBREW_CACHE should be reordered to have a format something like the following:
formula/version/source/file.tgz
formula/version/bottles/bottle.tar.gz
resources/resource-$SHA256.tar.gz
patches/patch.diff
This will allow simplifying the cleanup of the cache without needing to know as much about formula state.