Developer documentation

The current one written by Meuuh is badly outdated. Writing of a new one with more data, restructured, has just started.

• Perhaps a skeletal module in each category (better explained that the dummy module)
  • what they need todo, the design decisions, possibilities, or options that drivers in a category might implement
• If there is a canonical module for each category or modules that show the range of options that might be mentioned too.