[Packager] Allow user to specify a custom transformer file

[johanneslumpe]

This is an edited re-submission of #1458 because I'm stupid.

[sebmck]

This is only available on very recent node (0.12) and io.js versions. What's the supported version for the packager?

[johanneslumpe]

Oh that's odd. If we have to support older version, we might add

path.resolve(transformerPath) === path.normalize(transformerPath)

[amasad]

We want to support v0.10 (after all jest doesn't run on v0.12 yet). We have a package installed for this absolute-path

[amasad]

Just fix the absolute-path thing and this should be good to go.

[johanneslumpe]

@amasad done!

[amasad]

Great! Will do pull it. It'd be nice to add some docs to that as well :) 💃

[johanneslumpe]

@amasad are those docs fine?

[amasad]

We don't really have to wait on all interpreters. We can just end the sentence at by allowing you to use new JavaScript language features.

[amasad]

Sorry for the late reply. Just a few nits on the docs

[johanneslumpe]

@amasad updated the docs. I actually didn't write those texts, but they're changed the way you wanted now :)