`--library` option for inexecutable code

[nyuichi]

By the current design when jsx is passed no compiler options via command line arguments it compiles the code without emitting bootstrap code. This kind of behavior is pretty confusing especially for the case where compiling the same file many times in the terminal. To avoid the problem, we change jsx command in the following ways:

1. warn or throw an error when compiler doesn't take any option.
2. if you want to compile the code to create a shared (main function-free) js, you explicitly pass a compiler option --library.

--library is a very clear word for me but may not be for someone else. If you think --library sounds like an option to switch the external library path, any other ideas for the word is of course welcome.

[gfx]

Is it just to check syntax? If so, --test is enough, I think.

[nyuichi]

@gfx No, I don't mean that.

When I write a code which has a main routine to do something

// hello.jsx
class _Main {
  static function main(args : string[]) : void {
    log "hello";
  }
}

and then compile it so that I run the code later

$ jsx --output hello.jsx.js hello.jsx

But sometimes I forget to pass --executable node and the compiler doesn't complain anything about that, so something really bad will happen:

$ node hello.jsx.js
$ 

# nothing is happened, nothing is printed! WTF!

I just want to remove this really fucking behavior from the compiler.