Meira Refactor (#14566)

* clean up keyboard header files

* use #pragma once include guard
* convert tabs to spaces
* remove redundant #include statements
* update revision references to main header (`../meira.h` -> `meira.h`)

* refactor default keymap

* use LAYOUT as layout macro reference
* use enum statement for layer indexes; make layers contiguous
* use four-space indent
* update keycode grid alignment

* update layout macro aliases

* move layout macro aliases to info.json
  * alias KEYMAP to LAYOUT_ortho_4x12 so the user keymaps don't have to be edited

* touch up meira.h

There's no Planck MIT layout reference here.

* add copyright headers

* workaround patch for grahampheath keymap

The `matrix_init_kb()` function in `meira.c` calls `backlight_set()`, but the grahampheath keymap disables Backlight to make space for Audio, causing the firmware to fail to compile.

This commit wraps the `backlight_set()` call in an ifdef statement, so the call is excluded if Backlight is disabled.

* clean up rules.mk inline comments

* re-order rules.mk settings

* clean up readme.md

* correct link to keyboard image
* change metadata section to unordered list
* spelling corrections
* update make instructions and Docs links

keyboards/meira/info.json

@@ -2,6 +2,10 @@
     "keyboard_name": "Meira",
     "url": "",
     "maintainer": "colemarkham",
+    "layout_aliases": {
+        "KEYMAP": "LAYOUT_ortho_4x12",
+        "LAYOUT": "LAYOUT_ortho_4x12"
+    },
     "layouts": {
         "LAYOUT_ortho_4x12": {
             "layout": [