Update configuration file

Closes #66 (closed)

These changes update the configuration file format and also adds new pages for the website.

The configuration file can now define the Lua generator.

{
  // Output code in different ways depending on the given generator
  "generator": "retain-lines", // default value

  // "process" is deprecated and has been aliased to "rules"
  "rules": [
    // ...
  ],
}

Checklist:

• add entry to changelog
• update relevant documentation
• don't forget testing 😉