* Allows "gaps" for keyboards like Kyra.
* Allows keyboards with matrixes that don't map the logical key
locations to have normal looking keymaps when defined.
* Start of work of focusing on out-of-tree user keymaps.
Add ZMK_CONFIG support.
* General external configuration supported via ZMK_CONFIG,
which should point to a configuration directory.
* Priority order of overlay files to select.
* ${SHIELD}_${BOARD}.overlay
* ${SHIELD}.overlay
* ${BOARD}.overlay
* default.overlay
* Equivalent search order for .conf files for initial Kconfig
values.
