Add a filter before adding page to the cache

[vdwijngaert]

Hello,

First of all: love your plugin. Does what it needs to do and not bloated!

Here's my idea: I would love to be able to minimize the HTML output of my pages before they are being added to the cache. This could easily be achieved if you allowed the page to be altered before you store it in the cache. I think adding a simple filter would allow this in a gracious way.

I'll provide a pull request asap, I hope you'll take a look at it so others can benefit this too!

Sincerely,

Koen