add "parseFrom" and exit(1) on error

This is the last of my changes, I think!

It adds "parseFrom" from the google protobuf library, which we use a lot internally to unpack messages from byte arrays. I added the 4 method signatures that I thought were most likely to be used -- there are about 10 in the google package.

This also causes scalabuff to exit(1) if it threw any exceptions while running. It will still catch-and-continue, but when it's done, it will exit(1) to let the build tools know that it actually failed.