Adds support for native TW2.0 dark-mode (via class) & theme with CSS variables

[kenotron]

Fixes #53

I'm a fan of this repo, so I made a fork that has support for TW2.0 dark mode. The way it is put together isn't very friendly to someone who might want to use this in real life, maybe? The tailblocks.css in /public is the one you want to use, it's only 25k pre-gzipped.

I wrote a buuuunch of scripts that will merge the current light & dark .js files into one merged .js file. I also added support for theme through css variables. Take a look:

https://github.com/kenotron/tailblocks

If there's interest from @mertJF, I can make a PR, but the change is extensive:

added acorn / acorn-walk & family to get dark-mode class names merging working
replaced ${props.theme} with a CSS variable based one
added a tailwind.css.js, postcss, cssnano + a yarn css script that will generate a custom css that includes dark mode + css vars
run yarn css to regenerate the tailblocks.css