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/.travis.yml

@@ -0,0 +1,32 @@
+language: go
+
+go:
+ - 1.10.x
+ - 1.11.x
+ - master
+
+os:
+ - linux
+ - osx
+
+matrix:
+  include:
+   - os: osx
+     go: 1.7.5
+     env:
+      - GOFLAGS="-tags kqueue"
+  allow_failures:
+   - go: tip
+
+env:
+  global:
+   - GOBIN=$HOME/bin
+   - PATH=$HOME/bin:$PATH
+
+install:
+ - go get -t -v ./...
+
+script:
+ - "(go version | grep -q 1.4) || go tool vet -all ."
+ - go install $GOFLAGS ./...
+ - go test -v -timeout 60s -race $GOFLAGS ./...