[Keymap] rootiest for planck/rev6/ (#13294)

* squashed commits to master

* Fix in case of missing user_song_list
Substitutes missing songs with safe versions
Also updated and added detail to keymap readme

* Adjust Readme to match qmk contrib conventions

* Update keyboards/planck/keymaps/rootiest/config.h

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

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

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

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

* Fixed license header to GPLv2+

* Fix Volume key delay
Use a static number instead of removed MEDIA_KEY_DELAY

* Use TAP_CODE_DELAY

* added license to config.h

* Clean up formatting
- Fixed markdown in readme
- Removed extra commented line from config.h

* Update keyboards/planck/keymaps/rootiest/config.h

keyboards/planck/keymaps/rootiest/readme.md

@@ -0,0 +1,37 @@
+
+![Layout Image](https://github.com/rootiest/rootiest.github.io/raw/main/img/rootiest-planck_legend.png)
+
+# The Rootiest Planck Layout
+
+This layout takes advantage of as many QMK features as possible for a huge complicated beast of a keyboard!
+
+## Features include
+
+- Encoder functions further extended by layers and modifiers
+- Extensive use of the on-board speaker
+- Extensive use of the backlight LEDs for startup animations, layer indicators, and bootloader/debug warnings, etc
+- Many layers, both toggled and momentary.
+- A toggled Numpad layer, with an emphasis on coding/accounting and with arrow keys on WASD
+- A "Tabular" layer accessed by holding Tab with frequently used functions, including Alt+Tab via pressing Space
+- A toggled Mouse-keys layer that allows full control of the mouse movement and buttons from the keyboard
+- Use of Space-Cadet Shift/Ctrl keys on various layers
+- Hold enter for Right-Shift
+- Shift+BackSpace for Delete
+- Grave-Esc in the top-left Esc key position
+- Music, Terminal, MIDI, and RGB control on Functions layer
+- QWERTY, COLEMAK, DVORAK, and PLOVER layers
+- Special keys for common Ctrl+ combos like Ctrl+C, Ctrl+V, etc
+- Special keys for Copy-Line, Cut-Line, Delete-Line, etc
+- Special keys for Ctrl+Alt+Del, Alt+F4, etc
+- Settings like rgb animation state and startup animation/sound are stored in the EEPROM to survive restart
+- "Sticky keys" with audible indication allow most modifiers to be locked by pressing multiple times in quick succession
+- Sticky-locking the Shift key toggles CapsLock instead of locking Shift
+- Unicode characters and emoji can be sent via custom tap-dance keys
+- Emoji and app-specific functions can be sent via leader-key chording
+- VelociKey and word-per-minute tracking are also included
+
+See the layout here: [Keyboard Layout](http://www.keyboard-layout-editor.com/#/gists/e48e19bc251a8d07ff8475fc1a16f43b)
+
+To build and flash this keymap, use this command:
+
+    qmk flash -kb planck/rev6 -km rootiest