Remove Zepto JS, convert to vanilla JS

Hi,

I really like what you did with Whoops it really brings exception analysis to a new level.

I wanted to contribute something and I created the pure vanilla Javascript version of the PrettyPageHandler.
This means that it only contains the necessary JS codes, the browser support is the same as with Zepto JS

Also it is very small (just a little more than 1KB for the compressed version)

Keep up the good work !