Move example to _example for tests

If ./example/ has code non compilable code in it from a truss run, then
go test ./... will exit non 0 from this code failing to build. This is
annoying when testing truss on the example and then trying to rerun the
tests. This fixes it by adding the _ to avoid go's tooling

README.md

@@ -56,7 +56,7 @@ for HTTP 1.1/JSON transport!
 Then you open the `handlers/server/server_handler.go`, 
 add you business logic, and you're good to go.
 
-Here is an example service definition: [Echo Service](./example/echo.proto)
+Here is an example service definition: [Echo Service](./_example/echo.proto)
 
 Try Truss for yourself on Echo Service to see the service that is generated: