all: Become a Go module (fixes #5148) (#5384)

* 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

vendor/github.com/syncthing/notify/README.md

@@ -0,0 +1,22 @@
+notify [![GoDoc](https://godoc.org/github.com/rjeczalik/notify?status.svg)](https://godoc.org/github.com/rjeczalik/notify) [![Build Status](https://img.shields.io/travis/rjeczalik/notify/master.svg)](https://travis-ci.org/rjeczalik/notify "inotify + FSEvents + kqueue") [![Build status](https://img.shields.io/appveyor/ci/rjeczalik/notify-246.svg)](https://ci.appveyor.com/project/rjeczalik/notify-246 "ReadDirectoryChangesW") [![Coverage Status](https://img.shields.io/coveralls/rjeczalik/notify/master.svg)](https://coveralls.io/r/rjeczalik/notify?branch=master)
+======
+
+Filesystem event notification library on steroids. (under active development)
+
+*Documentation*
+
+[godoc.org/github.com/rjeczalik/notify](https://godoc.org/github.com/rjeczalik/notify)
+
+*Installation*
+
+```
+~ $ go get -u github.com/rjeczalik/notify
+```
+
+*Projects using notify*
+
+- [github.com/rjeczalik/cmd/notify](https://godoc.org/github.com/rjeczalik/cmd/notify)
+- [github.com/cortesi/devd](https://github.com/cortesi/devd)
+- [github.com/cortesi/modd](https://github.com/cortesi/modd)
+- [github.com/syncthing/syncthing-inotify](https://github.com/syncthing/syncthing-inotify)
+- [github.com/OrlovEvgeny/TinyJPG](https://github.com/OrlovEvgeny/TinyJPG)