Add support for browserify-shim

[ForbesLindesay]

First of all, thanks for the contribution!

A couple of things I'd like to get fixed before we can release this:

• The changes to bundleFile need to be applied to bundleModule as well
• The default value of the shim option should be false or null rather than {}, otherwise shim will be used even when there is nothing to shim.
• The option needs documentation - along with a link the the browserify-shim module.
• The functionality should have a unit test, just something that demonstrates that it seems to be working, it doesn't need to be exhaustive.

[ForbesLindesay]

browserify-shim now acts as a transform, so this is no longer needed.

[tristanstraub]

Things move quickly :)

[ForbesLindesay]

indeed they do :)