Implements Istanbul coverage support and user-defined sourceTransformers

[searls]

This PR addresses #25. Three changes in this PR:

1. CoffeeScript support is abstracted into a new object called a sourceTransformer as opposed to being hard-coded with the _getCompileInfo() method
2. Istanbul support for code coverage is added using the same means.
3. Arbitrary user-defined source transformers may be configured with a sourceTransformers option passed to SandboxedModule.require.

I was sure to add unit tests to cover everything I did. I tried to write everything I added in a manner that was congruent with the existing code.

Suggestions:

• Right now requiring coffeescript and istanbul isn't cached between SandboxedModule.require invocations (and hadn't been previously, either. It may be significantly more performant to memoize those methods.

[davemo]

:+1:

[domenic]

This looks very good. I only have the one comment, about how making Istanbul a new default might not be great, and also that the defaults should be configurable project-wide (so e.g. people who want to use, say, traceur, should be able to add a traceur source transformer once instead of on every require).

Also, since I am no longer actively using this module, if @felixge is OK with it, I think it'd be cool to add you as a maintainer on GitHub and npm, continuing the chain of custodion-ship transfer that started when @felixge handed this off to me :).

[felixge]

This looks very good. I only have the one comment, about how making Istanbul a new default might not be great, and also that the defaults should be configurable project-wide (so e.g. people who want to use, say, traceur, should be able to add a traceur source transformer once instead of on every require).

I agree with Dominic, but since I'm not actively maintaining this module right now, I'm not feeling strongly about it ; ).

Also, since I am no longer actively using this module, if @felixge is OK with it, I think it'd be cool to add you as a maintainer on GitHub and npm, continuing the chain of custodion-ship transfer that started when @felixge handed this off to me :).

Done. @searls you now have github / npm push access! Feel free to merge this patch once you're happy with it.

[searls]

Thanks @felixge & @domenic. I'm going to take a look at implementing two pieces of your feedback before merging this.

1. Allow this new option (and possibly any option) to be set globally instead of only on each-and-every-require
2. Make Istanbul (and presumably any new interceptors beyond CoffeeScript) opt-in. Figuring out a scheme that's both obvious and simple may be challenging (for instance, a plugin module system would be a little heavyweight, especially since we don't need to pull in the istanbul dependency in order to provide this support).

[searls]

Okay, I've made both those changes. Hopefully being able to set an app-wide global or require() stubbing will be of use to people even if the sourceTransformers & istsanbul stuff doesn't serve them. :smile:

I'll merge and push a version, bumping minor.

[searls]

Ping @felixge -- it looks like I don't have Github Push access to this repo, after all :)

[felixge]

@searls that's weird, it seems like GitHub forgot that I added you. Did you get an e-mail you were added? Anyway, I just added you again, should work now.

[searls]

Thanks folks. Released as 0.3.0.

[felixge]

:sparkling_heart: thx!