Better hot reload

[theRealProHacker]

Let's say an author changes the contents of a style element in the HTML file and that is currently loaded. Then the style element's content should be changed and that's it. Basically, the algorithm is just like React's algorithm to determine the difference between a new virtual DOM.

For this to work, we need to somehow find the difference in the new and old file versions DOM's and only update differences.

[theRealProHacker]

Depends on #58