IE8 Support

I have successfully gotten a full pass in IE8 for reactive. To do so, I needed to include #158, make some small adjustments to tests and code, and include a ton of shims. I did this by creating a separate repository: [reactive-ie8-shims](/yanatan16/reactive-ie8-shims), which can be included via browserify or prebuilt scripts. Simply shim it in before running any reactive code and you're golden!