Add support for custom css modules name patterns

[devongovett]

Closes #156.

This adds support for custom patterns for generating names in css modules. Using cssModules: true continues to use the same default pattern as before, but you can also now set it to a config object:

{
  cssModules: {
    pattern: 'library-[name]-[hash]-[local]
  }
}

The currently supported segments are:

• [name] - the base name of the file name being transformed, without the extension
• [hash] - a hash of the full file path
• [local] - the original class name

We could add more if needed as well. The pattern is parsed ahead of time and interpreted when writing out class names. Hopefully this solves the majority of use cases. We could add a JS callback for this as well, but it would add a lot of performance overhead so I would like to avoid it if possible.

[joelmoss]

Was this new functionality added to the rust CLI?