Adding "variable" option for JSONP and tools for Java configuration

Hey,

Here are some modifications that I think can be really useful to some of us.

### Variable option, commit d8f5f2c

We can now either require a callback to be returned or we can choose to have the JSON value set in a variable. Example: `var myvariable = {"foo": "bar"};`
I have seen this option in some APIs and I'll propose that in my projects.

### Java config, commit 76c6574

I don't use `web.xml` in some of my projects and choose to have a full Java config. To simplify my work, I added a constructor and setters that can be used to define the parameter names.

Are those modifications ok for you?

Thanks,