Adding autoSwitch for diff browsers proofer

[juandelperal]

This enables the automatic switching of fonts (new vs old) every 1.25 secs.
This helps to compare the versions without clicking all the time.

If the user clicks the old/new button, then the switching stops.

Demo:

PS. I couldn't test it compiles the HTML properly, just added the snippets in the template

[m4rc1e]

Sorry for not looking at this sooner.

[m4rc1e]

Seems the toggle has been broken for the other pages. I get the following traceback if I open up a page other than proofer.html

Uncaught ReferenceError: autoSwitch is not defined
    at HTMLDivElement.switchFonts (Black-Bold-ExtraBold-Medium-diffbrowsers_waterfall.html:638:25)

Since I like the feature, I don't mind fixing this but it may take me a while to get round to it.

[juandelperal]

Nice!
I can help with it. How do I build or run tests locally?

[juandelperal]

I (blindly) added a possible fix, but I cant generate the HTMLs properly
I tried using
python src/diffenator2/__main__.py diff -fb ...

but it seems that I'm getting a cached version, as the generated htmls don't show the changes I am trying