Added a shortcuts module

This is a first stab, but it works decent enough from the testing I did. It'd be cool to make these configurable or toggle-able or something. 

Also, I added jquery to the content scripts section, which probably wasn't necessary but I don't think the performance problems are going to be too terrible for anybody using chrome. 

Let me know what you think.
I don't think I can push changes to your fork, but I did something like this locally:
```
	function jumpToNextPost(){
		if( $("#Post" + (currentPostNumber + 1)).length > 0 ){	
			$("#Post" + currentPostNumber).css({"border-left-width": 1, "padding-left": 11});
			currentPostNumber++;
			location.hash = 'Post'+currentPostNumber;
			$("#Post" + currentPostNumber).css({"border-left-width": 3, "padding-left": 10});
		}
	};
```


And then:
```
	function jumpToPreviousPost(){
		if( $("#Post" + (currentPostNumber - 1)).length > 0 ){	
			$("#Post" + currentPostNumber).css({"border-left-width": 1, "padding-left": 11});
			currentPostNumber--;
			location.hash = 'Post'+currentPostNumber;
			$("#Post" + currentPostNumber).css({"border-left-width": 3, "padding-left": 10});
		}
	}
```