The default driver type is just an index into a device array defined
by the board.
If a platform wants to encode additional information in the device type,
it can define a custom type.
This means we can just set the default type to whatever fits the target
CPU best.
On ARM this will still be a 32 bit word, but on AVR it will by a 8 bit byte.
- unify file/module @brief
- distinct @file section more visibly in source
- provide missing @brief's
- move module details/notes from file to module sections
- provide missing macro definition for building
