Add support for app.browserify.options.json

[stubailo]

You can now create a file to pass options to browserify, including transforms. The transforms can be loaded from NPM in the same way as other dependencies.

It's going to be used in the new React in Meteor guide, preview here: http://react-in-meteor.readthedocs.org/en/latest/client-npm/

TODO

• write documentation for this new feature
• squash commits

[stubailo]

Sample options file to use global React when require("react") is called.

(helpful for using React Router with a global React)

{
  "transforms": {
    "exposify": {
      "global": true,
      "expose": {
        "react": "React"
      }
    }
  }
}

[stubailo]

@elidoran I think this is ready now. It's actually pretty hard to write automated tests for this feature, but I ran some apps to verify that things work. If you want, I can put in some more effort to write better tests, but they will probably be in the form of a second package that uses this one (that way we can test the build plugin more directly)

[elidoran]

I've committed changes on top of your PR.

1. I added a test for options with transforms
2. I added in the exorcist module to extract the source map and give it to CompileStep.
3. added a note in the README about adding the options file via api.addFiles()

I tested these in my example app as well.

I haven't published it as 0.4.0 yet. Please take a look.

[stubailo]

@elidoran looks awesome. Thanks for cleaning everything up and adding tests! Excited to use these new features.

[stubailo]

@elidoran please let me know when you publish the new version!

[elidoran]

@stubailo published as 0.4.0

[stubailo]

Stellar. Thanks for the quick turnaround.