Adding a basic sanity testing tool to run during 'build'.

The tool just runs 'go vet' for now; could do more later (like actually
run the examples and compare to some expected output)

tools/build

@@ -2,6 +2,7 @@
 
 set -e
 
+tools/test
 tools/format
 tools/measure
 tools/generate

tools/test

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# Sanity testing of the examples.
+
+set -eo pipefail
+
+# go vet will attempt to build each example, making sure it compiles. It will
+# also report known issues with the code. Disabling the -unreachable check
+# because it will fire false positives for some examples demonstrating panics.
+go vet -unreachable=false ./examples/...