[Keymap] snowkuma Planck keymap (#6225)

[Keymap] snowkuma Planck keymap (#6225)

* Snowkuma's planck layout.

Heavily influenced by both Planck and SDOTHUMs layouts.  I have tried to
implement a comfortable layout with a wide stagger and a minimal set of
key usage.

Still a work in progress, hope it is useful to others.

* Adds simple readme file and images of layout

* Removes unused experimental definitions

* Update readme.md

Adds images of layout to readme.

* Removes accidentally added test keymap .swn .swo .swp files

* Updates config.h replaces include guard

As suggested by @noroadsleft replaces the include guard (ifndef, define
and endif) with just `#pragma once`.

* Replaces two extra KC with inbuilt QMK equivalents

custom_keycodes.h
Replaces `___f___` with the equivalent QMK alias `_______` KC_TRNS
`___x___` with the equivalent QMK alias `XXXXXXX` KC_NO

Updates keymap.c to reflect the changes made.

* Changes keymap.c to include QMK_KEYBOARD_H

Replaces planck.h and action_layer.h includes with the single inclusion
of QMK_KEYBOARD_H which includes action_layer.h automatically.

* Update keyboards/planck/keymaps/snowkuma/keymap.c

Co-Authored-By: noroadsleft <18669334+noroadsleft@users.noreply.github.com>
* Update keymap.c

removes unused Coleman key code from enum planck_keycodes

* Update keymap.c removes COLEMAK key code logic