Lets patches be laid out as android/<version>/<real-aosp-path>/*.patch
and still land in the correct project, instead of every patch under a
mapped folder going to one fixed target.
local_manifests values are normally a single URL. The remove_projects
key may instead be a list of URLs, merged/de-duplicated into a single
manifest fragment rather than one file per key. Document repo.yml
structure in README and add a fully commented example.repo.yml.