add api for other pipelines

[goto-bus-stop]

Some plugins, like factor-bundle and browserify-dynamic-import, create multiple output files. These plugins typically expose an event that you can hook into to change their pipelines. It would be neat to have a simple way to add tinyify's relevant optimizations to a pipeline, maybe like this:

b.on('factor.pipeline', function (file, pipeline) {
  tinyify.applyToPipeline(pipeline)
})

tinyify could also hardcode event handlers like that in the main plugin, to make it a bit easier to use—just add -p tinyify to a project that uses factor-bundle and browserify-dynamic-import and get optimizations on all outputs immediately.

[yoshuawuyts]

Yeah this sounds heaps tricky — but would be very neat if it could be figured out!