Leader key implementation (#326)

* implements leader key for planck experimental

* allows override of leader timeout

* adds ability to use the leader key in seq

* fixes leader keycode

* adds chording prototype

* fixes keycode detection

* moves music mode to quantum.c

* disables chording by default

* updates process_action functions to return bool

Merge remote-tracking branch 'upstream/master'

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware

Backlight Breathing for Planck and Atomic

* Updated personal layouts

* tweaked personal

* Nightly - Audio Cleanup

Refactored the LUTs. Abstracted some of the registers out of audio to
use more functional names. Split audio into audio and audio_pwm. WIP

* nightly - collapsed code

* Added check for note playing to LEDs

* Usability tweaks

* TWEAE

* nightly

added extra kcs to keymap common

* turned on Plank audio

* Added backlight breathing to atomic

* reverted accidental merge

* adds backlight pulse to planck

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware

moves backlight functionality to keyboard files and updates template makefile

previously there were two backlight.c files (bad)

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware

Merge pull request #262 from IBNobody/master

Fixed keyboard snoring while asleep

Merge remote-tracking branch 'refs/remotes/origin/personal_atomic_planck'

Merge branch 'personal_atomic_planck' of github.com:IBNobody/qmk_firmware

Added extra songs, LED indicator notes

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware into modifier-release-fix

Merge branch 'master' of https://github.com/jackhumbert/tmk_keyboard

Merge remote-tracking branch 'jackhumbert/master' into make-keymap-names-consistent

Merge remote-tracking branch 'jackhumbert/master' into improve-buildguide

Merge pull request #3 from jackhumbert/master

Pull upstream

Merge branch 'master' of https://github.com/jackhumbert/qmk_firmware

Merge remote-tracking branch 'refs/remotes/jackhumbert/master'

# Conflicts:
#	quantum/template/template.c
#	quantum/template/template.h

Merge pull request #190 from yoyoerx/function_pointers

Addressing void* return warning & coding style