This implements a new plugin for Dynamic (EEPROM-stored) macros. Unlike the
Macros plugin, these macros are stored in EEPROM, and can't run custom code,
only the steps outlined in the Macros documentation.
The plugin provides two Focus commands (`macros.map` and `macros.trigger`) to
get or set the dynamic macros, and to trigger one without having to place them
on the keymap.
Fixes#370.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>