Add option for using the isUsingIjData flag

[mairatma]

This is similar to #38, but related to the --isUsingIjData flag right now. There's currently no way to it on the compiler through soynode, since there's no option for it.

Missing flags like this make me think that maybe soynode could instead have an easy way to pass flags, without having to have an option for each of them. That would probably mean a bigger change though, just thought it'd be good to mention.

So for now I have this working with an extra option on a local branch of mine, I'll send a pull request with it soon.