Added gentoo to installer (#3272)

* Added gentoo installer

* Remove comments

* Remove comments

* Updating the layout

* Revert "Remove comments"

This reverts commit e348afa41a470d4b8f1865d92b85acd32ab14074.

* Revert "Updating the layout"

This reverts commit 181822d195f722f4981825ded7dd85fa268c3c56.

* Undo erroneous revert

allow building with nix on darwin
add avrdude do dependency list

Overhaul to keycode related docs

* Adds Audio Keycodes to both the feature page and master list
* Re-orders the keycode list, so it's alphabetical (mostly)
* Add additional (missing) sections to the keycode list
* Add and update links in the keycode page
* Add and reorder links in sidebar's keycode section

Integrating Peter Fleury's HD44780 LCD library (#3209)

* integrated Peter Fleury's LCD library for HD44780 LCDs

* fixed typo

* cleanup finished

* add documentation

* added HD44780 documentation

* removed keyboard from .gitmodules

* resolved merge conflict

* removed edit of kira75s rules.mk made by merge

* moved hd44780 to drivers/avr

* Added licence info to hd44780 files

* Added link to hd44780 docs.

Fix tapdance when one-shot is disabled.

Update config.h boilerplate to use `#pragma once`

According to @fredizzimo, this is a safer and easier way to handle the
boilerplate.

Add Userspace mention

@drashna mentioned it'd be good to have a mention of the userspace in
the QMK structure section. Rather than rewrite the docs on userspace, I
chose to link to the existing documentation.

Reword the `config.h` section

This section didn't include the possibility of a user `config.h`, and it
wasn't clear exactly how the settings override works.

Update docs: `Makefile` -> `rules.mk`

I think this was a typo, or perhaps an older way to handle it.

Add I2C slave library

- Add I2C slave library for general use.

Added M10-B implementation

Added pin C6 to hardware PWM backlight

AJP10304 Atreus 50 layout (#3403)

UK78 Refactor: rename LAYOUT to LAYOUT_all (#3405)

UK78 refactor and Configurator support (#3395)

* Matrix update

* Keymap refactor

* Configurator support

* Readme cleanup

callum keymap updates (#3402)

* change window focus shortcuts

* hangul

* macos goodness

* re-arrange tab keys

* remove tab switching keys

* left hand func

* glorious macro pad

* workspace rotation keys

* tabbing hotkeys

mitosis:datagrok layout and readme improvements (#3400)

* mitosis:datagrok: improved tenkey layout; changelog + more in README

* mitosis:datagrok enable audio!

* mitosis:datagrok: underscore on right shift, rearrange some symbols

* mitosis:datagrok: add more descriptions to readme

* mitosis:datagrok: abuse space cadet to get equivalent of RSFT_T(KC_UNDS)

Add A Planck keymap with easier shifts and nav (#3399)

keymap BFO9000 built as 6x18 (#3398)

Configurator does not work with melody96 leds (#3396)

* move out led code from keymap.c to melody96.c

* remove the other led_set_user