* go mod init; rm -rf vendor
* tweak proto files and generation
* go mod vendor
* clean up build.go
* protobuf literals in tests
* downgrade gogo/protobuf
Given that we've taken on the resposibility of maintaining this forked
package I've added it to the Syncthing organization. We still vendor it
like an external package, because it's convenient to keep it as a fork
of upstream to easier merge and file pull requests towards them.
