package with browserify

We talked about some of these things over IRC and I wanted to submit another set of small patches for review along these lines.

* emitter-component vs emitter is a disaster. Please, just be consistent, use the github install way if you want but don't do this nonsense :)

* lib-cov is not needed. istanbul (and other coverage tools) can run without instrumentation steps. Maybe consider having mocha has an istanbul provider for coverage (they have an API). In either case, this does not belong in the code.

* xmlhttprequest replacement: instead of doing environment checks in the source (messy and error prone) just let the bundler "do the right thing" This leads to more reusable and clear code.

The end effect of the above changes is a reduction of final code size by about 3.6K for the engine.io.js dist file you guys create. That isn't a big deal, but what is a big deal is that you don't need to list all fo the js files over and over again in package.json or component.json. We have better tools ;)