Convert aos over to flatbuffers

Everything builds, and all the tests pass.  I suspect that some entries
are missing from the config files, but those will be found pretty
quickly on startup.

There is no logging or live introspection of queue messages.

Change-Id: I496ee01ed68f202c7851bed7e8786cee30df29f5
diff --git a/aos/util/file.h b/aos/util/file.h
index 385aba7..5d354a7 100644
--- a/aos/util/file.h
+++ b/aos/util/file.h
@@ -12,6 +12,10 @@
 // encountered.
 ::std::string ReadFileToStringOrDie(const absl::string_view filename);
 
+// Creates filename if it doesn't exist and sets the contents to contents.
+void WriteStringToFileOrDie(const absl::string_view filename,
+                            const absl::string_view contents);
+
 }  // namespace util
 }  // namespace aos