Add support for inline sourcemaps in jsx executable

I kept the option as `--source-map-inline` based on #833. I'm going to punt on the external part, though that should be easy now with `transformWithDetails` also being in react-tools.

I think it's important we get this in before 0.11 since we support sourcemaps in some form everywhere else and it's clowny not to do it in our own executable.

(I didn't update the readme yet, but I will)