Make CI verify that runtime library+generated code are matching
Add an "ExampleTests" directory to let Travis verify that the latest combination of runtime library+generated code are matching (i.e. don't produce any build errors).
I'm not 100% sure yet whether this works as expected, but I figured it would make sense to start by sending a pull request and see what Travis makes out of this ;-)
At the moment, running `swift build` in `ExampleTests` creates the file `ExampleTests/Generated/echo.grpc.swift`, and I have no idea why. Any suggestions on where that might come from would be much appreciated :-)
Daniel Alm