fix: tailwindcss content sources

[cossssmin]

This PR fixes a performance issue where we always included ./src/**/*.* in the content array when compiling Tailwind CSS.

This not only included a very broad pattern, but started significantly slowing builds down as more files were added to the src folder. It was especially noticeable when image (or other large binary) files were added to ./src/images.

Now, the default content sources are:

content: {
  files: [
    './src/components/**.html',
    './src/layouts/**.html',
    {raw: html, extension: 'html'}
  ]
}

... where html is the HTML string currently being processed.

If you add your own content key to tailwind.config.js, this will be overwritten to:

{
  files: [
    ...config.content,
    {raw: html, extension: 'html'}
  ]
}

... meaning that you need to make sure to also add any paths to Components or Layouts:

// tailwind.config.js

module.exports = {
  content: [
    './src/components/**.html',
    './src/layouts/**.html',
    // other content sources...
  ],
}