returns a path pointing to the folder containing .repo,
or io::Error in case the .repo folder couldn’t been
found in the cwd or any of its parent folders.
The repo-tool keeps a list of synced projects at
.repo/project.list
This function can filter the list of projects by groups
and/or manifest files. If a group and manifest filter
are given, the list will contain the intersection.
Additionally the function can include the manifest repo
itsself into the list (.repo/manifests).