Instead of a low-level interface where one has to set the EEPROM-stored layers
and the lookup method separately, introduce a `setup` method that combines the
two in a much easier to grasp interface. It takes a layer number, and an
optional mode, and sets things up accordingly.
With this new setup procedure comes a new way of how the plugin works: instead
of being able to override the keymap in EEPROM, we extend it (or use a custom
implementation, for advanced use-cases). The default layer can still be set via
Focus, thus effectively overriding the keymap in PROGMEM. To better support
this, a new Focus command is introduced too: `keymap.roLayers`, which returns
the number of layers in PROGMEM.
The `keymap.transfer` Focus command is removed, because it can be done much more
reliably from the host side, building on top of `keymap.map`.
The rest of the lower-level interface is still there, though undocumented, for
advanced use-cases the new simplified setup does not fit.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>
Gergely Nagy
83f1805d5d