doc(web_workers): fixes some typos and adjusts formatting

Closes #4425

modules/angular2/docs/web_workers/web_workers.md

@@ -75,9 +75,9 @@ run specifically on the UI or Worker. Additionally, they contain the core messag
 communicate between the Worker and the UI. This messaging code is not in the standard angular2.js file.
 * We pass `loader.js` to bootstrap and not `app.ts`. You can think of `loader.js` as the `index.html` of the
 Worker. Since WebWorkers share no memory with the UI we need to reload the angular2 dependencies before
-bootstrapping our application. We do this with importScripts. Additionally, we need to do this in a different 
+bootstrapping our application. We do this with `importScripts`. Additionally, we need to do this in a different
 file than `app.ts` because our module loader (System.js in this example) has not been loaded yet, and `app.ts`
-will be compiled with a System.define call at the top.
+will be compiled with a `System.define` call at the top.
 * The HelloWorld Component looks exactly like a normal Angular2 HelloWorld Component! The goal of WebWorker
 support was to allow as much of Angular to live in the worker as possible.
 As such, *most* angular2 components can be bootstrapped in a WebWorker with minimal to no changes required.
@@ -143,7 +143,7 @@ The main exception is that there is **no** DOM access from a WebWorker component
 import anything from `dart:html` and in JavaScript it means you can't use `document` or `window`. Instead you
 should use data bindings and if needed you can inject the `Renderer` along with your component's `ElementRef`
 directly into your component and use methods such as `setElementProperty`, `setElementAttribute`,
-`setElementClass`, `setElementStyle`, `invokeElementMethod`, and `setText`. Not that you **cannot** call
+`setElementClass`, `setElementStyle`, `invokeElementMethod`, and `setText`. Note that you **cannot** call
 `getNativeElementSync`. Doing so will always return `null` when running in a WebWorker.
 If you need DOM access see [Running Code on the UI](#running-code-on-the-ui).
 
@@ -277,7 +277,7 @@ class MyComponent {
 The only substantial difference between these APIs in Dart and TypeScript is the different APIs for the
 `EventEmitter`.
 
-**Note** Because the messages passed through the MessageBus cross a WebWorker boundary, they must be serializable.
+**Note:** Because the messages passed through the MessageBus cross a WebWorker boundary, they must be serializable.
 If you use the MessageBus directly, you are responsible for serializing your messages.
 In JavaScript / TypeScript this means they must be serializable via JavaScript's
 [structured cloning algorithim](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm).
@@ -298,7 +298,7 @@ change detection. Generally, you want your channels to run inside the zone unles
 they need to run outside the zone.
 
 ### Implementing and Using a Custom MessageBus
-**Note** Implementing and using a Custom MesageBus is experimental and requires importing from private APIs.
+**Note:** Implementing and using a Custom MessageBus is experimental and requires importing from private APIs.
 
 If you want to drive your application from something other than a WebWorker you can implement a custom message
 bus. Implementing a custom message bus just means creating a class that fulfills the API specified by the
@@ -338,7 +338,7 @@ class JsonMessageBusSource extends GenericMessageBuSource {
 }
 ```
 
-Once you've implemented your custom MessageBus in either TypeScript or Dart you can tell angular to use it like 
+Once you've implemented your custom MessageBus in either TypeScript or Dart, you can tell angular to use it like
 so:
 In TypeScript:
 ```TypeScript
@@ -390,8 +390,11 @@ because `bootstrapWebWorker` assumes you're using the default angular MessageBus
 ## MessageBroker
 The MessageBroker is a higher level messaging abstraction that sits on top of the MessageBus. It is used when you
 want to execute code on the other side of a runtime boundary and may want to receive the result.
-There are two types of MessageBrokers. The `ServiceMessageBroker` is used by the side that actually performs
-an operation and may return a result. Conversely, the `ClientMessageBroker` is used by the side that requests that
+There are two types of MessageBrokers:
+
+1. The `ServiceMessageBroker` is used by the side that actually performs
+an operation and may return a result;
+2. The `ClientMessageBroker` is used by the side that requests that
 an operation be performed and may want to receive the result.
 
 ### Using the MessageBroker In Your Application