* add matrix_diagram.md
* refactor default keymap
- use four-space indent
- grid-align keycodes
- use QMK-native keycode alias for `RGB_MODE_RGBTEST`
* refactor default_iso keymap
- use four-space indent
- grid-align keycodes
* refactor via keymap
- use four-space indent
- grid-align keycodes
- use QMK-native keycode alias for `KC_TRNS`
* info.json: apply friendly formatting
* add maintainer and url keys to info.json
* add LAYOUT_ansi with reference keymap
* add LAYOUT_iso; refactor default_iso keymap
* standardize default and via keymaps
- use `QK_GESC` at top left
- use `KC_DEL` for right half of Split Backspace
- use `KC_NUHS` for Non-US Hash position
- use `KC_NUBS` for Non-Us Backslash position
- use `KC_RGUI` for middle right mod
* add RGB Underglow keycodes to all keymap Function layers
