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/gopkg.in/asn1-ber.v1/.travis.yml

@@ -0,0 +1,18 @@
+language: go
+go:
+    - 1.2
+    - 1.3
+    - 1.4
+    - 1.5
+    - 1.6
+    - 1.7
+    - 1.8
+    - tip
+go_import_path: gopkg.in/asn-ber.v1
+install:
+    - go list -f '{{range .Imports}}{{.}} {{end}}' ./... | xargs go get -v
+    - go list -f '{{range .TestImports}}{{.}} {{end}}' ./... | xargs go get -v
+    - go get code.google.com/p/go.tools/cmd/cover || go get golang.org/x/tools/cmd/cover
+    - go build -v ./...
+script:
+    - go test -v -cover ./...