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/lib/pq/TESTS.md

@@ -0,0 +1,33 @@
+# Tests
+
+## Running Tests
+
+`go test` is used for testing. A running PostgreSQL
+server is required, with the ability to log in. The
+database to connect to test with is "pqgotest," on
+"localhost" but these can be overridden using [environment
+variables](https://www.postgresql.org/docs/9.3/static/libpq-envars.html).
+
+Example:
+
+	PGHOST=/run/postgresql go test
+
+## Benchmarks
+
+A benchmark suite can be run as part of the tests:
+
+	go test -bench .
+
+## Example setup (Docker)
+
+Run a postgres container:
+
+```
+docker run --expose 5432:5432 postgres
+```
+
+Run tests:
+
+```
+PGHOST=localhost PGPORT=5432 PGUSER=postgres PGSSLMODE=disable PGDATABASE=postgres go test
+```